Ink jet recorder

ABSTRACT

An ink jet recorder includes a support unit configured to support a recording medium, and a mobile unit including a plurality of containers containing inks of identical composition and a head configured to eject the ink supplied from any one of the plurality of containers. The ink jet recorder is configured to record an image on the recording medium in such a manner that the head performs main scanning by ejecting the ink while changing positions in a first direction, and the mobile unit performs sub-scanning by moving in a second direction intersecting with the first direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional patent application of U.S. application Ser. No.14/217,597 filed Mar. 18, 2014, which claims priority to Japanese PatentApplication Nos. 2013-065768, filed Mar. 27, 2013 and 2013-181902, filedSep. 3, 2013 all of which are expressly incorporated by reference hereinin their entireties.

BACKGROUND

1. Technical Field

The present invention relates to ink jet recorders.

2. Related Art

Ink jet recorders perform recording of data such as images on recordingmedia by ejecting fine ink droplets through nozzles of an ink jetrecording head. Such ink jet recorders have various structures inaccordance with the types and sizes of the recording media used.

For example, JP-A-2012-45909 discloses a so-called serial ink jetrecorder. A serial ink jet recorder has a head which is movable in afirst direction (the width direction of the recording surface of arecording medium), and performs recording of images by moving therecording medium in a second direction intersecting with the firstdirection while reciprocating the head in the first direction.

JP-A-2010-264624 discloses a flat-bed ink jet recorder. A flat-bed inkjet recorder has, for example, a panel configured to fix a recordingmedium, and a head which is movable in a first direction of therecording surface of the recording medium (the width direction of therecording medium) and in a second direction intersecting with the firstdirection. Images are recorded on the fixed recording medium while thehead is moved in the first direction and in the second direction. Inmost cases, such flat-bed ink jet recorders are used for the recordingon hard, heavy and frequently large-sized recording media such as glasssheets, acrylic sheets and metal sheets.

On the other hand, UV curable inks are widely used in ink jet recordingon such hard and heavy recording media because of their excellentweather resistance and water resistance. Ink jet recorders which recordimages with UV curable inks are usually equipped with an illuminator forcuring the inks deposited on the recording media. For example,JP-A-2010-23285 discloses a flat-bed UV (UV curable) ink jet recorder inwhich a UV illumination device is mounted on a mobile member (such as acarriage) together with a printing head.

Such flat-bed ink jet recorders described above sometimes have a mobileunit which is movable at least in the second direction, and the head ismounted on the mobile unit to attain movability in the second direction.

On the other hand, ink cartridges (containers) for supplying inks to thehead are often connected to the head via supply tubes. In such cases,the length of the supply tubes is preferably as short as possiblebecause the increase in the length of the supply tubes tends to raisethe probability of problems such as the entry of air and the increase inthe amount of precipitates of ink components. In order to reduce thelength of supply tubes, ink cartridges are sometimes mounted on themobile unit similarly to the head.

In the case where an ink cartridge mounted on a mobile unit has run outof the ink during recording of images, the recording of images has to beinterrupted for the exchange of ink cartridges. When the recording isresumed, however, it is often encountered that the colors of the imagesare different between before and after the resumption as well as thatthe mobile unit is misaligned during the exchange of ink cartridges,resulting in unsatisfactory images. Such failures of image recordingcause a significant loss particularly in the recording with a flat-bedink jet recorder because this type of recording usually involvesexpensive materials (for example, recording media such as acrylicsheets, and UV curable inks).

Meanwhile, UV curable inks exhibit high viscosity ascribed to thecomponents (for example, polymerizable compounds) and consequently havea difficulty in being ejected through a recording head at times. Thus,the UV curable inks are heated to lower the viscosity to a level suitedfor ejection before the inks are ejected through a recording head. Forexample, such heating of UV curable inks is performed with heating unitshaving a heater or the like which are disposed in, for example, therecording head, the containers containing the UV curable inks, and theink channels connecting the containers to the recording head.

On the other hand, the flat-bed ink jet recorder described abovesometimes has a mobile unit which is movable in the second direction(the direction intersecting with the width direction of the recordingsurface of a recording medium), and the head is mounted on the mobileunit to attain movability in the second direction. In this case, it ispreferable that the mobile unit be lightweight in order to remedy theload on devices such as a motor driving the mobile unit.

However, the weight of the mobile unit tends to be increased,particularly when UV curable inks are used, because components such asthe aforementioned UV illumination device and ink containers are oftenmounted on the mobile unit in addition to the recording head. In suchcases, further installation of the heating unit in the mobile unitsignificantly increases the load on devices associated with the mobileunit.

SUMMARY

Some aspects of the invention provide ink jet recorders which achieveexcellent recording continuity performance and can record satisfactoryimages by solving at least part of the aforementioned problems.

Other aspects of the invention provide, by solving at least part of theabove problems, ink jet recorders which realize a reduced load incurredduring the moving of a mobile unit even in the recording with UV curableinks.

The first aspect of the invention is aimed at solving at least part ofthe aforementioned problems, and may be realized in the forms of thefollowing embodiments or application examples.

Application Example 1

An ink jet recorder according to an aspect of the invention includes: asupport unit configured to support a recording medium, and a mobile unitincluding a plurality of containers containing inks of identicalcomposition, and a head configured to eject the ink supplied from anyone of the plurality of containers, the recorder being configured torecord an image on the recording medium in such a manner that the headperforms main scanning by ejecting the ink while changing positions in afirst direction, and the mobile unit performs sub-scanning by moving ina second direction intersecting with the first direction.

Application Example 2

In Application Example 1, the recorder may be configured such that whenthe amount of the ink contained in one of the plurality of containers isdecreased to or below a prescribed amount, the ink contained in anothercontainer is supplied to the head.

Application Example 3

In Application Example 1 or 2, the total of the initial volumes of theinks contained in the plurality of containers may be not more than 3500ml and the initial volume of the ink contained in each of the pluralityof containers may be not less than 500 ml, and the recorder may be usedfor the recording of an image on a recording medium having a recordingsurface with an area of 0.1 m² to 7 m².

Application Example 4

In any one of Application Examples 1 to 3, the mobile unit may includeone or more maintenance units configured to perform maintenance of thehead.

Application Example 5

In any one of Application Examples 1 to 4, the recorder may be free froma heating unit that heats the ink to obtain a viscosity suited forejection.

Application Example 6

In any one of Application Examples 1 to 5, the inks may be UV curableinks that are cured by UV illumination, and the mobile unit may includean illuminator including a UV emitting diode to induce curing of the UVcurable inks.

Application Example 7

In any one of Application Examples 1 to 6, the inks may be UV curableinks that are cured by UV illumination, and may contain an acylphosphineoxide compound as a photopolymerization initiator.

Application Example 8

In any one of Application Examples 1 to 7, the mobile unit may beconfigured to permit an input unit to be mounted thereon, image data tobe recorded on the recording medium being input into the input unit.

Application Example 9

In Application Example 4, the total mass of the maintenance unit(s)mounted on the mobile unit may be not more than 5 kg.

Application Example 10

In Application Example 4 or 9, the initial mass of the ink per onecontainer of the plurality of containers may be smaller than the totalmass of the maintenance unit(s) mounted on the mobile unit.

Application Example 11

In any one of Application Examples 1 to 10, the head and each of theplurality of containers may be connected to each other via a supplytube, and the length of the supply tube may be not more than 3.5 m.

The second aspect of the invention is aimed at solving at least part ofthe aforementioned problems, and may be realized in the forms of thefollowing embodiments or application examples.

Application Example 1

An ink jet recorder according to an aspect of the invention includes: asupport unit configured to support a recording medium, a containercontaining a UV curable ink, and a mobile unit including a headconfigured to eject the UV curable ink supplied from the container, themobile unit being free from a heating unit that heats the UV curable inkto lower the viscosity, the recorder being configured to record an imageon the recording medium in such a manner that the head performs mainscanning by ejecting the UV curable ink while changing positions in afirst direction, and the mobile unit performs sub-scanning by moving ina second direction intersecting with the first direction.

Application Example 2

In Application Example 1, the viscosity of the UV curable ink at 20° C.may be not more than 20 mPa·s.

Application Example 3

In Application Example 1 or 2, the UV curable ink may contain 40 mass %to 90 mass % of a monofunctional (meth)acrylate, and 5 mass % to 45 mass% of a difunctional or higher functional (meth)acrylate.

Application Example 4

In any one of Application Examples 1 to 3, the UV curable ink may be anonaqueous UV curable ink.

Application Example 5

In any one of Application Examples 1 to 4, the temperature of the UVcurable ink as ejected from the head may be not more than 35° C.

Application Example 6

In any one of Application Examples 1 to 5, the mobile unit may includean illuminator including a UV emitting diode to induce curing of the UVcurable ink.

Application Example 7

In Application Example 6, the illuminator may be configured to cure theUV curable ink deposited on the recording medium with illuminationenergy of 200 mJ/cm² to 1500 mJ/cm² by illuminating the ink with UVradiation having an emission peak wavelength in the range of 350 nm to420 nm.

Application Example 8

In any one of Application Examples 1 to 7, the UV curable ink maycontain a photopolymerization initiator, and the photopolymerizationinitiator may include an acylphosphine oxide compound.

Application Example 9

In any one of Application Examples 1 to 8, the mobile unit may includeone or more maintenance units configured to perform maintenance of thehead.

Application Example 10

In any one of Application Examples 1 to 9, the mobile unit may include adata processing section into which image data to be recorded on therecording medium is input and which converts the image data to a form ofdata suited for recording.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a block diagram illustrating a configuration of an ink jetrecorder according to an embodiment of the invention.

FIG. 2 is a perspective view schematically illustrating an ink jetrecorder according to an embodiment of the invention.

FIG. 3 is a schematic view illustrating a configuration for supplying anink from a container to a head in an ink jet recorder according to anembodiment of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Preferred embodiments of the first aspect of the invention will bediscussed below. The embodiments described below only illustrate someexamples of the invention, and the invention is not limited to suchembodiments. Various modifications are possible without departing fromthe scope of the invention.

1. Ink Jet Recorders

An ink jet recorder according to an embodiment of the invention includesa support unit that has a panel configured to support a recordingmedium, and a mobile unit that includes a plurality of containerscontaining inks of identical composition and a head configured to ejectthe ink supplied from any one of the plurality of containers. The inkjet recorder is configured to record an image on the recording medium insuch a manner that the head performs main scanning by ejecting the inkwhile changing positions in a first direction, and the mobile unitperforms sub-scanning by moving in a second direction intersecting withthe first direction.

Hereinbelow, configurations of the ink jet recorder and inks used in therecorder will be sequentially described in detail.

1.1. Recorder Configurations

The ink jet recorder in this embodiment is a so-called flat-bed ink jetrecorder configured to record an image on a supported recording mediumby moving the head in a first direction (in detail, the width directionon the recording surface of the recording medium) and in a seconddirection intersecting with the first direction (in detail, thedirection perpendicular to the first direction on the recording surfaceof the recording medium).

A structure of the ink jet recorder according to this embodiment will bedescribed in detail with reference to the drawings. The drawings may notbe to scale to help understanding of the structure of the ink jetrecorder of this embodiment.

FIG. 1 is a block diagram illustrating a configuration of an ink jetrecorder 1 (hereinafter, also referred to as “printer 1”) according tothis embodiment.

FIG. 2 is a perspective view schematically illustrating the ink jetrecorder 1 according to this embodiment. In FIG. 2, the first direction(the main scanning direction) is the width direction of the recordingsurface of a recording medium P placed on a panel 12, and coincides withthe direction in which a mobile unit 20 extends. The second direction(the sub-scanning direction) in FIG. 2 is the direction intersectingwith the first direction on the recording surface of the recordingmedium P, and coincides with the direction in which the mobile unit 20moves during recording.

As illustrated in FIG. 1, the printer 1 includes a support unit 10, amobile unit 20, detectors 100 and a controller 110. Image data is inputto an input unit 120. The printer 1 receives the image data, andcontrols the units through the controller 110. The controller 110controls the units based on the image data input from the input unit120, and an image is recorded on the recording medium P. The status inthe printer 1 is monitored with the detectors 100, and the detectors 100output the detection results to the controller 110. The controller 110controls the units based on the detection results output by thedetectors 100. Image data may be input to the input unit 120 from otherdevice that is not shown and be processed, for example, converted by theinput unit 120, and such processed image data may be passed from theinput unit 120 to the printer 1.

In more detail, the controller 110 is a control unit (a control section)for controlling the printer 1, and includes an interface section 112, aCPU 114, a memory 116 and a unit control circuit 118. The interfacesection 112 communicates data between the input unit 120 and the printer1. The CPU 114 is a processor for performing the control of the entiretyof the printer 1. The memory 116 ensures an area for storing theprograms of the CPU 114 as well as ensures a working area, and includesmemory elements such as RAM and EEPROM. The CPU 114 controls the unitsthrough the unit control circuit 118 according to the programs stored inthe memory 116.

The input unit 120 is a device into which image data to be recorded onthe recording medium P is input, and may be, for example, a personalcomputer or a touch-panel input device. The input unit 120 may include afunction that converts image data input from other devices.

As illustrated in FIG. 2, the input unit 120 may be mounted on themobile unit 20. In this manner, the length of wire cords connecting theinput unit 120 to the mobile unit 20 may be advantageously shortened.The mobile unit 20 is preferably configured to permit the input unit 120to be mounted thereon as is the case here. In detail, the mobile unit 20preferably includes a fixing section to which the input unit 120 isfixed, and a terminal through which the image data output from the inputunit 120 is input. Further, the input unit 120 may be mounted beforehandon the mobile unit 20. Such preliminary mounting is one embodiment ofthe mounting of the input unit 120.

Support Unit

In the embodiment illustrated in FIG. 2, the support unit 10 includes apanel 12 supporting a recording medium P, and thereby supports therecording medium P. During recording, the panel 12 of the support unit10 supports the recording medium P by acting on the side of therecording medium P opposite to a head 40 so as to ensure that therecording medium P will not be misaligned accidentally in the directionopposed to the head 40. In the embodiment illustrated in FIG. 2, thesupport unit 10 further includes a support table 14 supporting the panel12, and a suction unit 16 (for example, a vacuum pump or the like)disposed under the panel 12. Furthermore, the panel 12 has a pluralityof suction holes 13 connected to the suction unit 16. By operating thesuction unit 16, the recording medium P placed on the panel 12 isprevented from being misaligned accidentally on the panel 12 in theplane direction during recording. In the embodiment illustrated in FIG.2, the recording medium P is a transparent sheet medium having a sizecovering a region that includes all the suction holes 13 in the panel12. Although the suction unit 16 is illustrated as a unit that preventsthe recording medium P on the panel 12 from being accidentallymisaligned in the plane direction, the configuration is not limitedthereto as long as the recording medium P is not accidentally misalignedon the panel 12 in the plane direction during recording. For example,the recording medium P may be attached to the panel 12 via apressure-sensitive adhesive tape or the like. Alternatively, therecording medium P may be pressed with a pressing member giving apressure thereto from above or the sides of the recording medium P.Still alternatively, the recording medium P may be prevented from beingaccidentally misaligned on the panel 12 in the plane direction by theaction of its own weight. The support unit 10 is preferably located at afixed position where the ink jet recorder is disposed. The printer 1 maybe configured such that the recording medium P is transported over thepanel 12.

Mobile Unit

In the embodiment illustrated in FIG. 2, the mobile unit 20 includescontainers (ink cartridges) 30 containing inks, a head 40 configured toeject the ink supplied from the container 30, illuminators 50 disposedon both sides of the head 40 in the main scanning direction, a cap 60that can cover the ejection face of the head 40, an ink tray 65 thatwill receive the ink discharged during a flushing operation of the head40, and an input unit 120 into which image data is input. The cap 60 andthe ink tray 65 represent one embodiment of the maintenance units usedfor the maintenance of the head as will be described later.

The mobile unit 20 performs sub-scanning by moving in the seconddirection during the recording of an image on the recording medium P.The mobile unit 20 may be caused to move in the second direction by adriving unit (not shown), for example, a driving belt disposed along theend of the panel 12. However, the configuration is not limited theretoand any known driving unit may be used.

In the embodiment illustrated in FIG. 2, the mobile unit 20 includes acabinet 22. The head 40, the illuminators 50, the cap 60 and the inktray 65 are accommodated in the cabinet 22. In the case where the inksare UV curable inks described later, the accommodation of the head 40 inthe cabinet 22 is advantageous in that the ink attached to the nozzleface of the head 40 is suppressed from being cured by external light andconsequently the occurrence of problems such as ejection failure may bereduced.

Containers

The containers 30 are so-called ink cartridges in which inks arecontained. The containers 30 are detachably mounted on the mobile unit20.

The containers 30 and the head 40 may be connected via supply tubes (notshown). In this case, the ink in the container 30 is supplied to thehead 40 via the supply tube. The supply tubes are disposed for therespective containers 30, and may be, for example, plastic tube-shapedmembers (such as rubbers and elastomers).

The length of the supply tubes is preferably short because the increasein the length of the supply tubes tends to raise the probability ofproblems such as the entry of air in the supply tubes, the increase inthe amount of precipitates of ink components, and the increase in theamount of a cleaning solution required for cleaning. The length of thesupply tubes is preferably not more than 4 m, more preferably not morethan 3.5 m, and still more preferably not more than 3.0 m. In order toincrease the area of recording on the recording medium by extending thetravel distance of the head 40, the length of the supply tubes ispreferably not less than 1.0 m, more preferably not less than 1.5 m, andstill more preferably not less than 2 m.

The containers 30 may be mounted on the mobile unit 20 by being insertedinto a cartridge holder 32 disposed in the mobile unit 20. In theembodiment illustrated in FIG. 2, the containers 30 are disposed at theend of the mobile unit 20 in the first direction. However, theconfiguration is not limited thereto, and the containers 30 may bedisposed at any location in the mobile unit 20. While the containers 30are inserted along the second direction in the embodiment illustrated inFIG. 2, the cartridge holder 32 may be disposed at such a position thatthe containers 30 are inserted along the first direction.

The containers 30 may be mounted on a carriage 70 (described later). Inthe embodiment illustrated in FIG. 2, the containers 30 are not mountedon the carriage 70 (described later), but are mounted at a fixedposition in the mobile unit 20. When the containers 30 are mounted onother than the carriage 70 (described later), the load incurred duringthe moving of the carriage 70 may be reduced by the absence of theweight of the containers 30. Thus, it is preferable that the containers30 be mounted on the mobile unit at a location other than the carriage70 (described later) which carries the head 40 and is reciprocated inthe first direction.

In the embodiment illustrated in FIG. 2, ten containers 30 are arrangedin line along the main scanning direction. However, the arrangement ofthe containers 30 is not particularly limited.

Here, it is necessary that the ink jet recorder of the invention have aplurality of containers containing inks of identical composition. Duringrecording, the ink is supplied to the head from any one of the pluralityof containers containing the inks of identical composition. With thisconfiguration, recording may be performed continuously withoutinterruption for the exchange of containers even when any one of thecontainers has run out of the ink, because the ink of identicalcomposition may be supplied to the head from any of the othercontainers. As a result, the recording of images may be performedcontinuously for an extended period of time, in detail, until therecording of an image on any one recording medium is completed. Further,this configuration ensures satisfactory images by suppressing theoccurrence of problems such as that the colors of the images aredifferent between before and after the resumption of recording as wellas that the mobile unit is misaligned during the exchange of inkcartridges, resulting in misaligned images.

In the invention, the term “inks of identical composition” refers toinks containing the same components in the same contents. Inks havingthe same name may be regarded as the inks of identical composition.

FIG. 3 is a schematic view illustrating a configuration for supplying anink to a head 40A with a plurality of containers (containers 30A and30B) containing the inks of identical composition. As illustrated inFIG. 3, the containers 30A and 30B are connected to the head 40A via asupply tube 34A and a supply tube 34B. The supply tubes 34A and 34B areprovided with communication valves 35A and 35B that control the passageof the ink. The supply tubes 34A and 34B are connected to each otherdownstream (on the head 40A side from) the communication valves 35A and35B. That is, the channels defined by the supply tubes 34A and 34B mergewith each other at that point. Further, a feed pump 36 is disposeddownstream (on the head 40A side from) the confluence of the supplytubes.

To start the execution of image recording, first, the communicationvalve 35A is opened and thereafter the feed pump 36 is operated tosupply the ink in the container 30A to the head 40A. During thisprocess, the communication valve 35B is closed to block the supply ofthe ink from the container 30B. When the amount of the ink in thecontainer 30A is decreased to or below a prescribed amount (for example,when the remaining amount becomes 2% or below) during recording, thecommunication valve 35B is opened while closing the communication valve35A to supply the ink in the container 30B to the head 40A. In thismanner, one of the containers which has come close to the finish of theink during recording may be switched to another container to supply theink without interrupting the recording.

In the specification, the continuous supply of ink by switching a spentcontainer to a new container without any interruption of recording maybe sometimes referred to as the hot swapping function.

In the embodiment illustrated in FIG. 3, two containers containing inksof identical composition are illustrated. However, the configuration isnot limited thereto, and continuous recording may be performed similarlywith three or more containers containing inks of identical composition.

The ink jet recorder of the invention is preferably used for therecording of an image on a recording medium having a recording surfacewith an area of 0.1 m² to 7 m², more preferably 1 m² to 7 m², and stillmore preferably 2 m² to 6 m². The invention is particularly useful forthe recording on an area in the above range because such records arehighly visible when used in applications such as displays and alsobecause recording on a single sheet of recording medium requires largeamounts of inks. When the area of the recording surface is in the aboverange, the initial volume of the ink contained in each of the pluralityof containers containing the inks of identical composition is preferablynot less than 500 ml, more preferably not less than 600 ml, and stillmore preferably not less than 700 ml. Further, the total of the initialvolumes of the inks contained in the containers is preferably not morethan 3500 ml, more preferably not more than 3000 ml, and still morepreferably not more than 2000 ml. By limiting the initial volume of theink contained in each container to not less than 500 ml, the recordingof an image on a single recording medium may be completed withoutinterruption even when the recording surface of the recording medium hasthe above area. Further, the weight of the mobile unit may be reduced bylimiting the total volume of the inks contained in the containers to notmore than 3500 ml, thereby reducing the load incurred during the movingof the mobile unit.

The upper limit of the initial volume in each container is, although notlimited to, preferably not more than 1750 ml, more preferably not morethan 1500 ml, and still more preferably not more than 1000 ml. The lowerlimit of the total of the initial volumes in the containers is, althoughnot limited to, preferably not less than 1000 ml, more preferably notless than 1200 ml, and still more preferably not less than 1400 ml. Inthe invention, the initial volume refers to the volume of the inkcontained in the container before the use of the container.

Head

The head 40 has a nozzle face (not shown) disposed at a position opposedto the recording surface of the recording medium P, and ejects dropletsof the ink through a plurality of nozzles (not shown) disposed in thenozzle face to deposit the droplets onto the recording surface of therecording medium P.

In the embodiment illustrated in FIG. 2, the head 40 is mounted on thecarriage 70. The carriage 70 is attached by being supported by a guiderod 72 that is a support member spanned in the first direction, and isreciprocated by a carriage moving mechanism (not shown) in the firstdirection along the guide rod 72. The head 40 mounted on the carriage 70is reciprocated in the first direction by such movement of the carriage70. That is, recording on the recording medium P in the first directiontakes place by the ejection of the ink from the head 40 with themovement of the carriage 70.

In the embodiment illustrated in FIG. 2, the carriage 70 is illustratedas a member that moves the head 40 in the first direction (that is, thehead 40 is moved relative to the mobile unit 20). However, theconfiguration may be such that the mobile unit 20 itself is moved in thefirst direction in addition to the second direction (that is, the head40 is not moved relative to the mobile unit 20).

While the embodiment in FIG. 3 illustrates a configuration in which theink is supplied to the single head 40A from the plurality of containers(containers 30A and 30B) containing the inks of identical composition,the configuration is not limited thereto and may be such that heads aredisposed for the respective containers containing the inks of identicalcomposition. In this case, recording may be performed continuously byusing the second head communicating with the container 30B after thefinish of the supply of the ink to the first head communicating with thecontainer 30A.

Any ink jet recording system may be utilized in the head 40. Examples ofthe ink jet recording systems which may be used include a system inwhich a strong electric field is applied between the nozzles andaccelerating electrodes disposed ahead of the nozzles, then the ink iscontinuously ejected as droplets from the nozzles, and printinginformation signals are transmitted to the deflection electrodes whilethe ink droplets are flying between the deflection electrodes, or theink droplets are ejected in accordance with the printing informationsignals without deflection (electrostatic attraction system); a systemin which pressure is applied to the ink via a compact pump and the inkdroplets are forcibly ejected by mechanically oscillating the nozzleswith a crystal oscillator or the like; a system in which pressure andprinting information signals are applied simultaneously to the ink withpiezoelectric elements so as to eject the ink droplets and record animage (piezoelectric system); and a system in which the ink is heatedand bubbled with small electrodes in accordance with printinginformation signals so as to eject the ink droplets and record an image(thermal jet system).

Illuminators

The ink jet recorder of this embodiment preferably includes anilluminator in the case where UV curable inks that are cured by UVillumination are used.

In the embodiment illustrated in FIG. 2, illuminators 50 are disposed onthe carriage 70 that is mounted on the mobile unit 20, on both ends ofthe head 40 in the first direction. However, the configuration is notlimited thereto and the illuminators may be disposed at any locations aslong as UV radiation may be illuminated to the ink deposited on therecording surface of the recording medium P. For example, theilluminators may be disposed on the sides of the head 40 in the seconddirection so as to illuminate along the width direction (the firstdirection) of the recording medium, or such a configuration may be usedin combination with the illuminators 50 disposed at the positionsillustrated in FIG. 2.

The illuminator 50 includes a light source (not shown) and a lightsource controlling circuit (not shown) that controls switching on andoff of the light source. The light source is preferably a UV emittingdiode, in which case the increase in the size and weight of the lightsource may be avoided compared to when other light sources such asmercury lamps, metal halide lamps or other types of lamps are used.

When UV emitting diodes are used as the light sources, the wavelength ofemitted UV radiation may be appropriately in the range of about 360 to420 nm.

In order to increase the curing rate, to suppress the occurrence ofcuring wrinkles and to reduce the energy consumption, the illuminationintensity of the illuminators is preferably 500 mW/cm² to 2000 mW/cm²,and more preferably 700 mW/cm² to 2000 mW/cm².

In the curing step in which the ink is cured by illumination with theilluminators, the illumination energy is preferably 100 mJ/cm² to 2000mJ/cm², more preferably 200 mJ/cm² to 1500 mJ/cm², still more preferably200 mJ/cm² to 1000 mJ/cm², and particularly preferably 200 mJ/cm² to 800mJ/cm² in order to ensure sufficient curing and to reduce the energyconsumption.

Maintenance Unit

The ink jet recorder of this embodiment preferably has a maintenanceunit. The maintenance unit is a mechanism used for the maintenance ofthe head to prevent the occurrence of problems such as nozzle clogging.The maintenance unit is preferably mounted on the mobile unit, wherebythe head may be maintained during the driving of the mobile unit.

Examples of the operations for the maintenance of the head 40 include amoisture retention operation in which the head 40 is capped with the cap60 to prevent the vaporization of the ink except when recording is beingperformed, a flushing operation in which the ink is discharged from thenozzles of the head 40 to the ink tray 65 to prevent the nozzle cloggingwith the viscous ink as well as to adjust the meniscus of the nozzlesand allow the ink to be normally ejected from the head 40, a vacuumoperation (head cleaning) in which after the head 40 is capped with thecap 60, a vacuum pump (not shown) is driven to forcibly suction theviscous ink and foreign matters such as dusts that have become attachedto the nozzles, and thereby the meniscus is adjusted to allow the ink tobe normally ejected from the head 40, and a wiping operation with apurge treatment in which the nozzle face of the head 40 is wiped with awiper (not shown) to remove the ink which has become attached around thenozzles or has become viscous as well as to destroy the meniscus of thenozzles and readjust the meniscus.

As illustrated in FIG. 2, the cap 60 is disposed at one end of themobile unit 20 in the first direction, and the ink tray 65 is disposedat the other end in the first direction. However, the configuration isnot limited thereto, and these members may be disposed at any locationsas long as they are mounted on the mobile unit 20 and do not interferewith the recording operation of the head 40.

In order to reduce the load incurred during the movement of the mobileunit 20, it is preferable that the maintenance units mounted on themobile unit 20 be lightweight. For example, the mass of the maintenanceunits is preferably not more than 5 kg, and more preferably not morethan 3 kg. The lower limit is, although not limited to, preferably notless than 0.5 kg, and more preferably not less than 1 kg.

Further, it is preferable that the initial mass of the ink per onecontainer be smaller than the mass of the maintenance units mounted onthe mobile unit 20. This configuration reduces the influence by theincreased mass of the mobile unit 20 due to the increase in the numberof containers as compared to by the mass of the maintenance units. Thus,the number of containers mounted on the mobile unit 20 may be increased.In this embodiment, the specific gravity of the ink is defined to beapproximately 1 and thus, when the initial volume of the ink in thecontainer is 700 ml, the initial mass is 700 g. When the specificgravity of the ink is other than 1, the initial mass of the ink may beobtained by multiplying the initial volume of the ink in the containerby the specific gravity of the ink.

The maintenance unit is any one or more of a cap 60, a vacuum pump (notshown), an ink tray 65 and a wiper (not shown). When two or more of suchunits are used, the mass of the maintenance units is the total mass ofthe units.

Others

The ink jet recorder according to this embodiment may include a heatingunit (such as a so-called electrical heater) to heat the ink and reducethe viscosity of the ink to a level suited for ejection. From theviewpoint of reducing the weight of the mobile unit 20, however, the inkjet recorder is preferably free from such a heating unit.

At the time of ejection, the viscosity of the ink is preferably not morethan 13 mPa·s. In the case where the ink jet recorder has no heatingunits, the temperature of the ink during ejection is varied depending onthe environment in which the ink jet recorder is placed. Provided thatthe temperature of the environment in which the ink jet recorder isplaced usually ranges from about 20° C. to 30° C., the viscosity of theink in this temperature range is preferably such that the ink may beejected without heating, in detail, not more than 13 mPa·s at 20° C.,more preferably in the range of 4 mPa·s to 13 mPa·s, and still morepreferably 7 mPa·s to 13 mPa·s. This viscosity advantageously ensuressatisfactory ejection and suppresses curing wrinkles. The ink viscositymay be measured with an E-type viscometer.

In order to control the ink viscosity in the above range, theproportions of components in the ink may be appropriately adjusted. Forexample, when UV curable inks described later are used, the viscositymay be controlled by controlling the proportions of polymerizablecompounds.

1.2. Inks

Any usual ink jet recording inks may be used in the ink jet recorder ofthis embodiment. However, the use of UV curable inks is preferablebecause images can be favorably recorded on such recording media asglasses, acrylics and metals. Although UV curable inks are often moreexpensive than usual ink jet recording inks, the ink jet recorder ofthis embodiment reduces the occurrence of recording failures and thussuppresses wasteful consumption of the inks.

Hereinbelow, the chemical compositions of UV curable inks as an exampleof the inks used in the ink jet recorder of this embodiment will bedescribed in detail.

1.2.1. Polymerizable Compounds

The inks in this embodiment may contain a polymerizable compound. Uponillumination with light, the polymerizable compound is polymerized byitself or by the action of a photopolymerization initiator describedlater, and the deposited ink is thus cured. The polymerizable compoundspreferably include at least a vinyl ether group-containing (meth)acrylicacid ester represented by General Formula (I) and/or anothermonofunctional (meth)acrylate. In the invention, the term “(meth)acrylicacid” refers to both acrylic acid and methacrylic acid, and the term“(meth)acrylate” refers to both acrylate and methacrylate.

The polymerizable compounds will be described in detail focusing onthese (meth)acrylates.

Vinyl Ether Group-Containing (Meth)Acrylic Acid Esters

The ink in this embodiment preferably includes a vinyl ethergroup-containing (meth)acrylic acid ester represented by General Formula(I) below.

CH₂═CR¹—COOR²—O—CH═CH—R³  (I)

In Formula (I), R¹ is a hydrogen atom or a methyl group, R² is adivalent organic residue having 2 to 20 carbon atoms, and R³ is ahydrogen atom or a monovalent organic residue having 1 to 11 carbonatoms.

The vinyl ether group-containing (meth)acrylic acid ester givesexcellent curability to the ink and lowers the viscosity of the ink.Further, the use of such a compound containing a vinyl ether group and a(meth)acrylic group in the molecule is more advantageous in achievinggood curability of the ink than the separate use of a compoundcontaining a vinyl ether group and a compound containing a (meth)acrylicgroup.

In General Formula (I), the divalent organic residue having 2 to 20carbon atoms which is represented by R² is preferably a linear, branchedor cyclic, and optionally substituted alkylene group having 2 to 20carbon atoms, an optionally substituted alkylene group having 2 to 20carbon atoms which has an oxygen atom derived from an ether bond and/oran ester bond in the structure, or an optionally substituted divalentaromatic group having 6 to 11 carbon atoms. Of these, alkylene groupshaving 2 to 6 carbon atoms such as ethylene group, n-propylene group,isopropylene group and butylene group; and alkylene groups having 2 to 9carbon atoms which have an oxygen atom derived from an ether bond in thestructure such as oxyethylene group, oxy-n-propylene group,oxyisopropylene group and oxybutylene group are preferably used.

In General Formula (I), the monovalent organic residue having 1 to 11carbon atoms which is represented by R³ is preferably a linear, branchedor cyclic, and optionally substituted alkyl group having 1 to 10 carbonatoms, or an optionally substituted aromatic group having 6 to 11 carbonatoms. Of these, alkyl groups having 1 to 2 carbon atoms such as methylgroup and ethyl group, and aromatic groups having 6 to 8 carbon atomssuch as phenyl group and benzyl group are preferably used.

For the organic residues which may be substituted, the substituents areclassified into groups having carbon atoms and groups having no carbonatoms. In the first case in which the substituents are groups havingcarbon atoms, the carbon atoms in the substituents are included in thenumber of the carbon atoms in the organic residues. Examples of thegroups containing carbon atoms include, although not limited to,carboxyl groups and alkoxy groups. In the second case, examples of thegroups having no carbon atoms include, although not limited to, hydroxylgroup and halo groups.

Examples of the vinyl ether group-containing (meth)acrylates include,although not limited to, 2-vinyloxyethyl (meth)acrylate,3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl(meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl(meth)acrylate, 1-methyl-3-vinyloxypropyl (meth)acrylate,1-vinyloxymethylpropyl (meth)acrylate, 2-methyl-3-vinyloxypropyl(meth)acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth)acrylate,3-vinyloxybutyl (meth)acrylate, 1-methyl-2-vinyloxypropyl(meth)acrylate, 2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl(meth)acrylate, 6-vinyloxyhexyl (meth)acrylate,4-vinyloxymethylcyclohexylmethyl (meth)acrylate,3-vinyloxymethylcyclohexylmethyl (meth)acrylate,2-vinyloxymethylcyclohexylmethyl (meth)acrylate,p-vinyloxymethylphenylmethyl (meth)acrylate,m-vinyloxymethylphenylmethyl (meth)acrylate,o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(vinyloxyethoxy)ethyl(meth)acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyethoxy)propyl (meth)acrylate, 2-(vinyloxyethoxy)isopropyl(meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyethoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyethoxy)propyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyethoxyethoxy)isopropyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)isopropyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,polyethylene glycol monovinyl ether (meth)acrylate, and polypropyleneglycol monovinyl ether (meth)acrylate.

Of these, 2-(vinyloxyethoxy)ethyl (meth)acrylate, namely, at least oneof 2-(vinyloxyethoxy)ethyl acrylate and 2-(vinyloxyethoxy)ethylmethacrylate is preferable, and 2-(vinyloxyethoxy)ethyl acrylate is morepreferable because these (meth)acrylates can decrease the ink viscosityto a lower level, have a high ignition point and are excellent in termsof curability of the ink. In particular, the ink viscosity can bedecreased to a markedly low level because 2-(vinyloxyethoxy)ethylacrylate and 2-(vinyloxyethoxy)ethyl methacrylate have simple structuresand low molecular weights. Examples of the 2-(vinyloxyethoxy)ethylmethacrylates include 2-(2-vinyloxyethoxyl)ethyl methacrylate and2-(1-vinyloxyethoxyl)ethyl methacrylate. Examples of the2-(vinyloxyethoxy)ethyl acrylates include 2-(2-vinyloxyethoxyl)ethylacrylate and 2-(1-vinyloxyethoxyl)ethyl acrylate. The2-(vinyloxyethoxy)ethyl acrylates outperform the 2-(vinyloxyethoxy)ethylmethacrylates in terms of curability.

The vinyl ether group-containing (meth)acrylic acid esters may be usedsingly, or two or more may be used in combination.

The content of the vinyl ether group-containing (meth)acrylic acidester, in particular, 2-(vinyloxyethoxy)ethyl (meth)acrylate, ispreferably 20 mass % to 90 mass %, more preferably 40 mass % to 80 mass%, and still more preferably 50 mass % to 75 mass % with respect to thetotal mass of the ink (100 mass %). This lower limit of the contentensures that the ink viscosity may be lowered and the curability of theink may be further enhanced. On the other hand, the upper limit of thecontent ensures that good storage stability of the ink may be maintainedand the occurrence of curing wrinkles may be prevented furthereffectively.

Examples of the methods for producing the vinyl ether group-containing(meth)acrylic acid esters include, although not limited to, theesterification of (meth)acrylic acid with a hydroxyl group-containingvinyl ether (production method B), the esterification of a (meth)acrylicacid halide with a hydroxyl group-containing vinyl ether (productionmethod C), the esterification of (meth)acrylic acid anhydride with ahydroxyl group-containing vinyl ether (production method D), thetransesterification between a (meth)acrylic acid ester and a hydroxylgroup-containing vinyl ether (production method E), the esterificationof (meth)acrylic acid with a halogen-containing vinyl ether (productionmethod F), the esterification of an alkali (or alkaline earth) metal(meth)acrylate with a halogen-containing vinyl ether (production methodG), the vinyl exchange reaction of a hydroxyl group-containing(meth)acrylic acid ester with vinyl carboxylate (production method H),and the ether exchange reaction of a hydroxyl group-containing(meth)acrylic acid ester with an alkyl vinyl ether (production methodI).

Of these methods, the production method E is preferable because theadvantageous effects according to this embodiment are enhanced.

Monofunctional (Meth)Acrylates

The ink in this embodiment preferably contains a monofunctional(meth)acrylate instead of or in addition to the vinyl ethergroup-containing (meth)acrylic acid ester. By containing themonofunctional (meth)acrylate, the ink shows a low viscosity and allowsa photopolymerization initiator and other additives to exhibit excellentsolubility in the ink. Further, the use of the monofunctional(meth)acrylate facilitates obtaining good ejection stability during inkjet recording, and enhances the toughness, the heat resistance and thechemical resistance of the obtainable records.

Examples of the monofunctional (meth)acrylates include phenoxyethyl(meth)acrylate, isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl(meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomyristyl(meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl-diglycol(meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl(meth)acrylate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol(meth)acrylate, methoxydiethylene glycol (meth)acrylate,methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol(meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl(meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate,lactone-modified flexible (meth)acrylate, t-butylcyclohexyl(meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl(meth)acrylate, benzyl (meth)acrylate, ethoxylated nonylphenyl(meth)acrylate, alkoxylated nonylphenyl (meth)acrylate, and p-cumylphenol EO-modified (meth)acrylate.

Of these, those monofunctional (meth)acrylates having an aromatic ringbackbone in the molecule are preferable because further improvements areobtained in curability, storage stability and solubility ofphotopolymerization initiators. Preferred examples of the monofunctional(meth)acrylates having an aromatic ring backbone include, although notlimited to, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate,2-hydroxyphenoxypropyl (meth)acrylate and phenoxydiethylene glycol(meth)acrylate. Of these, at least one of phenoxyethyl (meth)acrylateand benzyl (meth)acrylate is preferable, and phenoxyethyl (meth)acrylateis more preferable because the ink viscosity may be reduced as well asbecause excellent properties are obtained in terms of all of curability,abrasion resistance, adhesion and solubility of photopolymerizationinitiators.

The monofunctional (meth)acrylates other than the vinyl ethergroup-containing (meth)acrylic acid esters may be used singly, or two ormore may be used in combination.

The content of the monofunctional (meth)acrylate other than the vinylether group-containing (meth)acrylic acid ester is preferably 10 mass %to 50 mass %, and more preferably 20 mass % to 40 mass % with respect tothe total mass of the ink (100 mass %). This lower limit of the contentensures that the solubility of a photopolymerization initiator inaddition to curability will be further enhanced. On the other hand, theupper limit of the content ensures that the adhesion in addition tocurability will be further enhanced.

From such viewpoints as curability, suppression of curing wrinkles andsolubility of photopolymerization initiators, the content of the vinylether group-containing (meth)acrylic acid ester and/or themonofunctional (meth)acrylate other than the vinyl ethergroup-containing (meth)acrylic acid ester is preferably 40 mass % to 90mass %, more preferably 55 mass % to 80 mass %, and still morepreferably 60 mass % to 80 mass % with respect to the total mass of theink (100 mass %).

Additional Polymerizable Compounds

The ink in this embodiment may further contain a polymerizable compoundother than those described above (hereinafter, referred to as“additional polymerizable compound”). The additional polymerizablecompounds may be any of various known monofunctional, difunctional,trifunctional and higher functional monomers and oligomers. Examples ofthe monomers include unsaturated carboxylic acids such as (meth)acrylicacid, itaconic acid, crotonic acid, isocrotonic acid and maleic acid aswell as salts and esters thereof, urethanes, amides and anhydridesthereof, acrylonitrile, styrene, various unsaturated polyesters,unsaturated polyethers, unsaturated polyamides and unsaturatedurethanes. Examples of the oligomers include oligomers formed of theabove monomers such as linear acrylic oligomers, and epoxy(meth)acrylates, oxetane (meth)acrylates, aliphatic urethane(meth)acrylates, aromatic urethane (meth)acrylates and polyester(meth)acrylates.

Of the additional polymerizable compounds, difunctional and higherfunctional (meth)acrylic acid esters, namely, difunctional and higherfunctional (meth)acrylates are preferable, and difunctional tohexafunctional (meth)acrylates are more preferable.

Examples of the difunctional (meth)acrylates include diethylene glycoldi(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethyleneglycol di(meth)acrylate, polyethylene glycol di(meth)acrylate,dipropylene glycol di(meth)acrylate, tripropylene glycoldi(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanedioldi(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanedioldi(meth)acrylate, neopentyl glycol di(meth)acrylate,dimethylol-tricyclodecane di(meth)acrylate, bisphenol A EO (ethyleneoxide) adduct di(meth)acrylate, bisphenol A PO (propylene oxide) adductdi(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylate, andpolytetramethylene glycol di(meth)acrylate.

Examples of the trifunctional and higher functional (meth)acrylatesinclude trimethylolpropane tri(meth)acrylate, EO-modifiedtrimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate,pentaerythritol tetra(meth)acrylate, dipentaerythritolhexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerinpropoxy tri(meth)acrylate, caprolactone-modified trimethylolpropanetri(meth)acrylate, pentaerythritolethoxy tetra(meth)acrylate, andcaprolactam-modified dipentaerythritol hexa(meth)acrylate.

The additional polymerizable compounds may be used singly, or two ormore may be used in combination.

From such viewpoints as curability, suppression of curing wrinkles andsolubility of photopolymerization initiators, the content of theadditional polymerizable compound, if any contained in the ink, ispreferably 5 mass % to 45 mass %, more preferably 5 mass % to 35 mass %,and still more preferably 5 mass % to 30 mass % with respect to thetotal mass of the ink (100 mass %). In the case where the ink containsan additional polymerizable compound that is a trifunctional or higherfunctional (meth)acrylate, the content thereof is preferably 5 mass % to20 mass %, more preferably 5 mass % to 15 mass %, and still morepreferably 5 mass % to 10 mass % with respect to the total mass of theink (100 mass %).

Curing wrinkles are probably caused when the curing inside the inkproceeds slower than the curing of the ink surface and consequently theink surface is deformed by the progress of the curing inside the ink. Inthis embodiment, such curing wrinkles are advantageously suppressed whenthe ink contains a difunctional or higher functional (meth)acrylic acidester.

The addition of photopolymerization initiators may be omitted by usingphotopolymerizable compounds as the polymerizable compounds. However,the use of photopolymerization initiators is more advantageous becausethe initiation of polymerization may be easily controlled.

1.2.2. Photopolymerization Initiators

The ink in this embodiment may further contain a photopolymerizationinitiator. The photopolymerization initiator may be used to inducephotopolymerization by the illumination with radiation and to cure theink deposited on the recording surface of the recording medium, therebyforming a print. Of the radiations, ultraviolet (UV) radiation may beadvantageously used because of its safety as well as because the costsof light source lamps may be saved. The photopolymerization initiatorswhich may be used are not limited as long as active species such asradicals or cations are generated by the application of UV energy toinduce the polymerization of the polymerizable compounds. Radical orcation photopolymerization initiators may be used. In particular,radical photopolymerization initiators may be preferably used.

Examples of the radical photopolymerization initiators include aromaticketones, acylphosphine oxide compounds, aromatic onium salt compounds,organic peroxides, thio compounds (such as thioxanthone compounds andthiophenyl group-containing compounds), hexaarylbiimidazole compounds,ketoxime ester compounds, borate compounds, azinium compounds,metallocene compounds, active ester compounds, compounds having acarbon-halogen bond, and alkylamine compounds. Of these, acylphosphineoxide compounds are preferable because the curability of the ink may befurther enhanced particularly when UV emitting diodes are used.

Specific examples of the radical photopolymerization initiators includeacetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenylketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone,benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole,3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone,4,4′-diaminobenzophenone, Michler's ketone, benzoin propyl ether,benzoin ethyl ether, benzyl dimethyl ketal,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one,2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone,diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one,bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide,2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide,2,4-diethylthioxanthone, andbis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

Examples of commercially available radical photopolymerizationinitiators include IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethan-1-one),IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173(2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959(1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one),IRGACURE 127(2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propan-1-one),IRGACURE 907 (2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one),IRGACURE 369(2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1), IRGACURE379(2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone),DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE819 (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide), IRGACURE 784(bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium),IRGACURE OXE 01 (1,2-octanedione, 1-[4-(phenylthio)-,2-(0-benzoyloxime)]), IRGACURE OXE 02 (ethanone,1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(0-acetyloxime)),IRGACURE 754 (a mixture of oxyphenyl acetic acid2-[2-oxo-2-phenylacetoxyethoxy]ethyl ester and oxyphenyl acetic acid2-(2-hydroxyethoxyl)ethyl ester) (product names, manufactured by BASF),KAYACURE DETX-S (2,4-diethylthioxanthone) (product name, manufactured byNippon Kayaku Co., Ltd.), Speedcure TPO(2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), Speedcure DETX(2,4-diethylthioxanthen-9-one) (product names, manufactured by Lambson),Lucirin TPO, LR8893, LR8970 (product names, manufactured by BASF), andUBECRYL P36 (product name, manufactured by UCB).

The photopolymerization initiators may be used singly, or two or moremay be used in combination.

In order to ensure that the UV curing rate is increased and excellentcurability is obtained as well as to prevent incomplete dissolution ofthe photopolymerization initiator and to prevent coloring ascribed tothe photopolymerization initiator, the content of thephotopolymerization initiator is preferably not more than 20 mass % withrespect to the total mass of the ink (100 mass %). Particularly in thecase in which the photopolymerization initiator includes anacylphosphine oxide compound, the content thereof is more preferably 5mass % to 15 mass %, and still more preferably 7 mass % to 13 mass %with respect to the total mass of the ink (100 mass %). This lower limitof the content ensures that curability is further enhanced. In moredetail, the curability is further enhanced because a sufficient curingrate is obtained during curing particularly with UV emitting diodes(preferably having an emission peak wavelength of 360 nm to 420 nm). Onthe other hand, the upper limit of the content ensures that thesolubility of the photopolymerization initiator is further enhanced.

1.2.3. Coloring Materials

The ink in this embodiment may further contain a coloring material. Thecoloring material may be at least one of a pigment and a dye.

By using a pigment as the coloring material, the light resistance of theink may be enhanced. The pigments may be any of inorganic pigments andorganic pigments.

Examples of the inorganic pigments which may be used include carbonblacks (C.I. pigment black 7) such as furnace black, lamp black,acetylene black and channel black, iron oxide and titanium oxide.

Examples of the organic pigments include azo pigments such as insolubleazo pigments, condensed azo pigments, azo lakes and chelate azopigments; polycyclic pigments such as phthalocyanine pigments, peryleneand perinone pigments, anthraquinone pigments, quinacridone pigments,dioxane pigments, thioindigo pigments, isoindolinone pigments andquinophthalone pigments; dye chelates (such as basic dye chelates andacidic dye chelates), dye lakes (basic dye lakes and acidic dye lakes),nitro pigments, nitroso pigments, aniline blacks, and daylightfluorescent pigments.

The pigments may be used singly, or two or more may be used incombination.

When the pigment is used, the average particle diameter thereof ispreferably not more than 300 nm, and is more preferably 50 nm to 200 nm.This average particle diameter ensures that the ink is further enhancedin terms of reliability such as ejection stability and dispersionstability as well as that high quality images may be formed. In thespecification, the average particle diameter may be measured by adynamic light scattering method.

The dyes are not particularly limited, and any of acidic dyes, directdyes, reactive dyes and basic dyes may be used. The dyes may be usedsingly, or two or more may be used in combination.

1.2.4. Dispersants

In the case where the ink in this embodiment contains the pigment, theink may further contain a dispersant to enhance the dispersibility ofthe pigment. The dispersants are not particularly limited. For example,dispersants generally used to prepare pigment dispersions such aspolymer dispersants may be used. Specific examples thereof include thosewhich contain at least one main component selected from polyoxyalkylenepolyalkylene polyamines, vinyl polymers and copolymers, acrylic polymersand copolymers, polyesters, polyamides, polyimides, polyurethanes, aminopolymers, silicon-containing polymers, sulfur-containing polymers,fluorine-containing polymers and epoxy resins. Examples of commerciallyavailable polymer dispersants include AJISPER series (product names)manufactured by Ajinomoto Fine-Techno Co., Inc., Solsperse series (suchas Solsperse 32000 and 36000 (product names)) available from Avecia Co.,DISPERBYK series (product names) manufactured by BYK Chemie, andDISPARLON series (product names) manufactured by KUSUMOTO Chemicals,Ltd.

The dispersants may be used singly, or two or more may be used incombination. The content of the dispersants is not particularly limited,and the dispersants may be appropriately added in suitable amounts.

1.2.5. Polymerization Inhibitors

The ink in this embodiment may further contain a polymerizationinhibitor. The presence of a polymerization inhibitor in the inkprevents the polymerization reaction of the polymerizable compoundsbefore curing.

The polymerization inhibitors are not particularly limited. For example,phenolic polymerization inhibitors may be used. Examples of the phenolicpolymerization inhibitors include, although not limited to,p-methoxyphenol, cresol, t-butylcatechol, di-t-butylparacresol,hydroquinone monomethyl ether, α-naphthol,3,5-di-t-butyl-4-hydroxytoluene, 2,6-di-t-butyl-4-methylphenol,2,2′-methylene-bis(4-methyl-6-t-butylphenol),2,2′-methylene-bis(4-ethyl-6-butylphenol), and4,4′-thio-bis(3-methyl-6-t-butylphenol).

Examples of commercially available phenolic polymerization inhibitorsinclude p-methoxyphenol (manufactured by Tokyo Chemical Industry Co.,Ltd., product name, p-methoxyphenol), NONFLEX MBP (manufactured by SeikoChemical Co., Ltd., product name,2,2′-methylene-bis(4-methyl-6-t-butylphenol)) and BHT SWANOX(manufactured by Seiko Chemical Co., Ltd., product name,2,6-di-t-butyl-4-methylphenol).

The polymerization inhibitors may be used singly, or two or more may beused in combination. The content of the polymerization inhibitors is notparticularly limited, and the polymerization inhibitors may beappropriately added in suitable amounts.

1.2.6. Surfactants

The ink in this embodiment may further contain a surfactant. Thesurfactants are not particularly limited. For example, siliconesurfactants such as polyester-modified silicones and polyether-modifiedsilicones may be used. It is particularly preferable to usepolyether-modified polydimethylsiloxane or polyester-modifiedpolydimethylsiloxane. Examples of commercially available slipping agentsinclude BYK-347, BYK-348, and BYK-UV3500, 3510, 3530 and 3570(manufactured by BYK).

The surfactants may be used singly, or two or more may be used incombination. The content of the surfactants is not particularly limited,and the surfactants may be appropriately added in suitable amounts.

1.2.7. Other Additives

The ink in this embodiment may contain additives (components) other thanthe aforementioned additives. Such components are not particularlylimited. Examples include known polymerization accelerators, penetrationenhancers, wetting agents (humectants), and further additives. Examplesof the further additives include known fixing agents, mildew-proofingagents, preservatives, antioxidants, UV absorbers, chelating agents, pHadjusters and thickening agents.

1.2.8. Illumination Energy

When the UV curable inks described above are used, it is preferable touse such UV curable inks which are cured with illumination energy of notmore than 1000 mJ/cm², more preferably not more than 300 mJ/cm², stillmore preferably not more than 200 mJ/cm², and particularly preferablynot more than 100 mJ/cm² from the viewpoint that the power consumptionby the illuminators may be saved.

1.3. Recording Media

The ink jet recorder of this embodiment may be used for the recording onany types of recording media used in flat-bed ink jet recorders (such aspapers, woven articles, knitted articles, nonwoven fabrics, leathers,resin films, resin sheets, glasses and metals). On any of theserecording media, the ink jet recorder of the invention may producerecords with satisfactory image quality with a reduced probability offailures such as misaligned images or variations in color tone. Thus,the inventive ink jet recorder may be suitably used even for therecording on expensive recording media (such as metals, acrylics andglasses) where a significant loss is incurred in the event of recordingfailure.

The recording medium used in the flat-bed ink jet recorder is a singlesheet. For example, the length of the recording surface in the seconddirection when the sheet is supported on the panel of the support unit10 may be not more than 4 m, particularly not more than 3 m and may benot less than 0.5 m, particularly not less than 1 m.

Preferred embodiments of the second aspect of the invention will bediscussed below. The embodiments described below only illustrate someexamples of the invention, and the invention is not limited to suchembodiments. Various modifications are possible without departing fromthe scope of the invention.

1. Ink Jet Recorders

An ink jet recorder according to an embodiment of the invention includesa support unit configured to support a recording medium, a containercontaining a UV curable ink, and a mobile unit including a headconfigured to eject the UV curable ink supplied from the container, themobile unit being free from a heating unit that heats the UV curable inkto lower the viscosity. The ink jet recorder is configured to record animage on the recording medium in such a manner that the head performsmain scanning by ejecting the UV curable ink while changing positions ina first direction, and the mobile unit performs sub-scanning by movingin a second direction intersecting with the first direction.

Hereinbelow, configurations of the ink jet recorder and inks used in therecorder will be sequentially described in detail.

1.1. Recorder Configurations

The ink jet recorder in this embodiment is a so-called flat-bed ink jetrecorder configured to record an image on a supported recording mediumby moving the head in a first direction (in detail, the width directionon the recording surface of the recording medium) and in a seconddirection intersecting with the first direction (in detail, thedirection perpendicular to the first direction on the recording surfaceof the recording medium).

A structure of the ink jet recorder according to this embodiment will bedescribed in detail with reference to the drawings. The drawings may notbe to scale to help understanding of the structure of the ink jetrecorder of this embodiment.

FIG. 1 is a block diagram illustrating a configuration of an ink jetrecorder 1 (hereinafter, also referred to as “printer 1”) according tothis embodiment.

FIG. 2 is a perspective view schematically illustrating the ink jetrecorder 1 according to this embodiment. In FIG. 2, the first direction(the main scanning direction) is the width direction of the recordingsurface of a recording medium P placed on a panel 12, and coincides withthe direction in which a mobile unit 20 extends. The second direction(the sub-scanning direction) in FIG. 2 is the direction intersectingwith the first direction on the recording surface of the recordingmedium P, and coincides with the direction in which the mobile unit 20moves during recording.

As illustrated in FIG. 1, the printer 1 includes a support unit 10, amobile unit 20, detectors 100 and a controller 110. Image data is inputto an input unit 120. The printer 1 receives the image data, andcontrols the units through the controller 110. The controller 110controls the units based on the image data input from the input unit120, and an image is recorded on the recording medium P. The status inthe printer 1 is monitored with the detectors 100, and the detectors 100output the detection results to the controller 110. The controller 110controls the units based on the detection results output by thedetectors 100. Image data may be input to the input unit 120 from otherdevice that is not shown and be processed, for example, converted by theinput unit 120, and such processed image data may be passed from theinput unit 120 to the printer 1.

In more detail, the controller 110 is a control unit (a control section)for controlling the printer 1, and includes an interface section 112, aCPU 114, a memory 116 and a unit control circuit 118. The interfacesection 112 communicates data between the input unit 120 and the printer1. The CPU 114 is a processor for performing the control of the entiretyof the printer 1. The memory 116 ensures an area for storing theprograms of the CPU 114 as well as ensures a working area, and includesmemory elements such as RAM and EEPROM. The CPU 114 controls the unitsthrough the unit control circuit 118 according to the programs stored inthe memory 116.

The input unit 120 is a device into which image data to be recorded onthe recording medium P is input, and may be, for example, a personalcomputer (PC) or a touch-panel input device. The input unit 120 mayinclude a function that converts image data input from other devices.The input unit 120 is an example of the data processing section in theapplication examples. For example, the input unit 120 is a personalcomputer having a printer driver installed therein that controls the inkjet recorder. The input unit 120 (PC) performs data processing in whichthe image data before data processing (for example, JPEG format imagedata) is converted to a data format suited for the ink jet recorder torecord on the recording medium (for example, dot format image data).

As illustrated in FIG. 2, the input unit 120 may be mounted on themobile unit 20. In this manner, the length of wire cords connecting theinput unit 120 to the mobile unit 20 may be advantageously shortened.Thus, the mobile unit 20 is preferably configured to permit the inputunit 120 to be mounted thereon. In detail, the mobile unit 20 preferablyincludes a fixing section to which the input unit 120 is fixed, and aterminal through which the image data output from the input unit 120 isinput. Further, the input unit 120 may be mounted beforehand on themobile unit 20. Such preliminary mounting is one embodiment of themounting of the input unit 120.

Support Unit

In the embodiment illustrated in FIG. 2, the support unit 10 includes apanel 12 supporting a recording medium P, and thereby supports therecording medium P. During recording, the panel 12 of the support unit10 supports the recording medium P by acting on the side of therecording medium P opposite to a head 40 so as to ensure that therecording medium P will not be misaligned accidentally in the directionopposed to the head 40. In the embodiment illustrated in FIG. 2, thesupport unit 10 further includes a support table 14 supporting the panel12, and a suction unit 16 (for example, a vacuum pump or the like)disposed under the panel 12. Furthermore, the panel 12 has a pluralityof suction holes 13 connected to the suction unit 16. By operating thesuction unit 16, the recording medium P placed on the panel 12 isprevented from being misaligned accidentally on the panel 12 in theplane direction during recording. In the embodiment illustrated in FIG.2, the recording medium P is a transparent sheet medium having a sizecovering a region that includes all the suction holes 13 in the panel12.

Although the suction unit 16 is illustrated as a unit that prevents therecording medium P on the panel 12 from being accidentally misaligned inthe plane direction, the configuration is not limited thereto as long asthe recording medium P is not accidentally misaligned on the panel 12 inthe plane direction during recording. For example, the recording mediumP may be attached to the panel 12 via a pressure-sensitive adhesive tapeor the like. Alternatively, the recording medium P may be pressed with apressing member giving a pressure thereto from above or the sides of therecording medium P. Still alternatively, the recording medium P may beprevented from being accidentally misaligned on the panel 12 in theplane direction by the action of its own weight. The support unit 10 ispreferably located at a fixed position where the ink jet recorder isdisposed.

In order to transport the recording medium P over the panel 12, thesupport unit 10 may include a transport mechanism (such as transportrollers) that is not shown.

Mobile Unit

In the embodiment illustrated in FIG. 2, the mobile unit 20 includescontainers (ink cartridges) 30 containing inks, a head 40 configured toeject the ink supplied from the container 30, illuminators 50 disposedon both sides of the head 40 in the main scanning direction, a cap 60that can cover the ejection face of the head 40, an ink tray 65 thatwill receive the ink discharged during a flushing operation of the head40, and an input unit 120 into which image data is input, and the mobileunit 20 does not include any heating units described later. The cap 60and the ink tray 65 represent one embodiment of the maintenance unitsused for the maintenance of the head as will be described later.

The mobile unit 20 performs sub-scanning by moving in the seconddirection during the recording of an image on the recording medium P.The mobile unit 20 may be caused to move in the second direction by adriving unit (not shown), for example, a combination of a driving beltdisposed along the end of the panel 12, and a motor or the like.However, the configuration is not limited thereto and any known drivingunit may be used.

Although the embodiment in FIG. 2 illustrates a configuration in whichthe mobile unit 20 itself is moved in the second direction, theconfiguration is not limited thereto and may be such that the mobileunit 20 itself is moved in the first direction in addition to the seconddirection (that is, the head 40 is not moved relative to the mobile unit20).

In the embodiment illustrated in FIG. 2, the mobile unit 20 includes acabinet 22. The head 40, the illuminators 50, the cap 60 and the inktray 65 are accommodated in the cabinet 22. In the use of UV curableinks, in particular UV curable inks described later, the accommodationof the head 40 in the cabinet 22 is advantageous in that the inkattached to the nozzle face of the head 40 is suppressed from beingcured by external light and consequently the occurrence of problems suchas ejection failure may be reduced.

In the ink jet recorder of this embodiment, the mobile unit 20 does notcarry any heating units described later. Thus, the weight of the mobileunit may be saved, and consequently the load incurred during themovement of the mobile unit may be reduced.

Containers

The containers 30 are so-called ink cartridges in which UV curable inksare contained. In the embodiment illustrated in FIG. 2, the containers30 are detachably mounted on the mobile unit 20.

The containers 30 and the head 40 may be connected via supply tubes (notshown). In this case, the ink in the container 30 is supplied to thehead 40 via the supply tube. The supply tubes are disposed for therespective containers 30, and may be, for example, plastic tube-shapedmembers (such as rubbers and elastomers).

The length of the supply tubes is preferably short because the increasein the length of the supply tubes tends to raise the probability ofproblems such as the entry of air in the supply tubes, the increase inthe amount of precipitates of ink components, and the increase in theamount of a cleaning solution required for cleaning. In order to reducethe occurrence of problems associated with the inks or the cleaningsolution, the containers 30 are preferably disposed near the head 40while ensuring that the operation of the head 40 is not limited. Thus,as illustrated in FIG. 2, it is preferable that the containers 30 bemounted on the mobile unit 20 together with the head 40. In the casewhere the containers 30 are mounted on the mobile unit 20, the length ofthe supply tubes is preferably not more than 4 m, more preferably notmore than 3.5 m, and still more preferably not more than 3.0 m. In orderto increase the area of recording on the recording medium by extendingthe travel distance of the head 40, the length of the supply tubes ispreferably not less than 1.0 m, more preferably not less than 1.5 m, andstill more preferably not less than 2 m.

In contrast, the weight saving of the mobile unit 20 favors the absenceof the containers 30 on the mobile unit. The location of the containers30 may be determined in consideration of the aforementioned problemsduring recording. In the case where, for example, the components in theink are resistant to precipitation, the weight saving of the mobile unit20 may be prioritized and the containers 30 may be disposed at anyposition on the printer 1 except on the mobile unit 20.

In the embodiment illustrated in FIG. 2, the containers 30 are mountedon the mobile unit 20 by being inserted into a cartridge holder 32disposed in the mobile unit 20. In the embodiment illustrated in FIG. 2,the containers 30 are disposed at the end of the mobile unit 20 in thefirst direction. However, the configuration is not limited thereto, andthe containers 30 may be disposed at any location in the mobile unit 20.While the containers 30 are inserted along the second direction in theembodiment illustrated in FIG. 2, the cartridge holder 32 may bedisposed at such a position that the containers 30 are inserted alongthe first direction.

The containers 30 may be mounted on a carriage 70 (described later). Inthe embodiment illustrated in FIG. 2, the containers 30 are not mountedon the carriage 70 (described later), but are mounted at a fixedposition in the mobile unit 20. When the containers 30 are mounted onother than the carriage 70 (described later), the load incurred duringthe moving of the carriage 70 may be reduced by the absence of theweight of the containers 30. Thus, it is preferable that the containers30 be mounted on the mobile unit 20 at a location other than thecarriage 70 (described later) which carries the head 40 and isreciprocated in the first direction.

In the embodiment illustrated in FIG. 2, ten containers 30 are arrangedin line along the main scanning direction. However, the arrangement ofthe containers 30 is not particularly limited, and the number of mountedcontainers is not particularly limited.

Here, the ink jet recorder of this embodiment may have a plurality ofcontainers containing inks of identical composition. In this case, theink jet recorder is preferably configured such that, during recording,the ink is supplied to the head from any one of the plurality ofcontainers containing the inks of identical composition. With thisconfiguration, recording may be performed continuously withoutinterruption for the exchange of containers even when any one of thecontainers has run out of the ink, because the ink of identicalcomposition may be supplied to the head from any of the othercontainers. As a result, the recording of images may be performedcontinuously for an extended period of time, in detail, until therecording of an image on any one recording medium is completed. Further,this configuration ensures satisfactory images by suppressing theoccurrence of problems such as that the colors of the images aredifferent between before and after the resumption of recording as wellas that the mobile unit is misaligned during the exchange of inkcartridges, resulting in misaligned images.

In the invention, the term “inks of identical composition” refers toinks containing the same components in the same contents. Inks havingthe same name may be regarded as the inks of identical composition.

FIG. 3 is a schematic view illustrating a configuration for supplying anink to a head 40A with a plurality of containers (containers 30A and30B) containing the inks of identical composition. As illustrated inFIG. 3, the containers 30A and 30B are connected to the head 40A via asupply tube 34A and a supply tube 34B. The supply tubes 34A and 34B areprovided with communication valves 35A and 35B that control the passageof the ink. The supply tubes 34A and 34B are connected to each otherdownstream (on the head 40A side from) the communication valves 35A and35B. That is, the channels defined by the supply tubes 34A and 34B mergewith each other at that point. Further, a feed pump 36 is disposeddownstream (on the head 40A side from) the confluence of the supplytubes.

To start the execution of image recording, first, the communicationvalve 35A is opened and thereafter the feed pump 36 is operated tosupply the ink in the container 30A to the head 40A. During thisprocess, the communication valve 35B is closed to block the supply ofthe ink from the container 30B. When the amount of the ink in thecontainer 30A is decreased to or below a prescribed amount (for example,when the remaining amount becomes 2% or below) during recording, thecommunication valve 35B is opened while closing the communication valve35A to supply the ink in the container 30B to the head 40A. In thismanner, one of the containers which has come close to the finish of theink during recording may be switched to another container to supply theink without interrupting the recording.

In the specification, the continuous supply of ink by switching a spentcontainer to a new container without any interruption of recording maybe sometimes referred to as the hot swapping function.

In the embodiment illustrated in FIG. 3, two containers containing inksof identical composition are illustrated. However, the configuration isnot limited thereto, and continuous recording may be performed similarlywith three or more containers containing inks of identical composition.Further, two or more containers containing inks of identical compositionmay be disposed only for inks which are used more frequently.

In the ink jet recorder of the invention, the hot swapping function maybe omitted when the hot swapping function is not required. In such aconfiguration, every ink containers contain inks of differentcompositions. The effect of the inventive configuration in which themobile unit is free from any heating units is particularly appreciatedwhen the hot swapping function is added because the addition of such afunction increases the weight of the mobile unit 20.

The ink jet recorder of the invention is preferably used for therecording of an image on a recording medium having a recording surfacewith an area of 0.1 m² to 7 m², more preferably 1 m² to 7 m², and stillmore preferably 2 m² to 6 m². Records having an area in the above rangeare highly visible when used in applications such as displays. Further,the hot swapping function is particularly useful for such recordingbecause recording on a single sheet of recording medium requires largeamounts of inks.

When the area of the recording medium is in the above range and whenthere is a plurality of containers containing inks of identicalcomposition, the initial volume of the ink contained in each of thecontainers is preferably not less than 500 ml, more preferably not lessthan 600 ml, and still more preferably not less than 700 ml. Further,the total of the initial volumes of the inks contained in the containersis preferably not more than 3500 ml, more preferably not more than 3000ml, and still more preferably not more than 2000 ml. By limiting theinitial volume of the ink contained in each container to not less than500 ml, the recording of an image on a single recording medium may becompleted without interruption even when the recording surface of therecording medium has the above area. Further, the weight of the mobileunit may be reduced by limiting the total volume of the inks containedin the containers to not more than 3500 ml, thereby reducing the loadincurred during the moving of the mobile unit.

The upper limit of the initial volume in each container is, although notlimited to, preferably not more than 1750 ml, more preferably not morethan 1500 ml, and still more preferably not more than 1000 ml. The lowerlimit of the total of the initial volumes in the containers is, althoughnot limited to, preferably not less than 1000 ml, more preferably notless than 1200 ml, and still more preferably not less than 1400 ml. Inthe invention, the initial volume refers to the volume of the inkcontained in the container before the use of the container.

Head

The head 40 has a nozzle face (not shown) disposed at a position opposedto the recording surface of the recording medium P, and ejects dropletsof the ink through a plurality of nozzles (not shown) disposed in thenozzle face to deposit the droplets onto the recording surface of therecording medium P.

In the embodiment illustrated in FIG. 2, the head 40 is mounted on thecarriage 70. The carriage 70 is attached by being supported by a guiderod 72 that is a support member spanned in the first direction, and isreciprocated by a carriage moving mechanism (not shown) in the firstdirection along the guide rod 72. The head 40 mounted on the carriage 70is reciprocated in the first direction by such movement of the carriage70. That is, recording on the recording medium P in the first directiontakes place by the ejection of the ink from the head 40 with themovement of the carriage 70.

In the embodiment illustrated in FIG. 2, the carriage 70 is illustratedas a member that moves the head 40 in the first direction (that is, thehead 40 is moved relative to the mobile unit 20). However, theconfiguration may be such that the mobile unit 20 itself is moved in thefirst direction in addition to the second direction (that is, the head40 is not moved relative to the mobile unit 20).

While FIG. 3 illustrates a configuration in which the ink jet recorderin this embodiment has the hot swapping function and the ink is suppliedto the single head 40A from the plurality of containers (containers 30Aand 30B) containing the inks of identical composition, the configurationis not limited thereto and may be such that heads are disposed for therespective containers containing the inks of identical composition. Inthis case, recording may be performed continuously by using the secondhead communicating with the container 30B after the finish of the supplyof the ink to the first head communicating with the container 30A.

Any ink jet recording system may be utilized in the head 40. Examples ofthe ink jet recording systems which may be used include a system inwhich a strong electric field is applied between the nozzles andaccelerating electrodes disposed ahead of the nozzles, then the ink iscontinuously ejected as droplets from the nozzles, and printinginformation signals are transmitted to the deflection electrodes whilethe ink droplets are flying between the deflection electrodes, or theink droplets are ejected in accordance with the printing informationsignals without deflection (electrostatic attraction system); a systemin which pressure is applied to the ink via a compact pump and the inkdroplets are forcibly ejected by mechanically oscillating the nozzleswith a crystal oscillator or the like; a system in which pressure andprinting information signals are applied simultaneously to the ink withpiezoelectric elements so as to eject the ink droplets and record animage (piezoelectric system); and a system in which the ink is heatedand bubbled with small electrodes in accordance with printinginformation signals so as to eject the ink droplets and record an image(thermal jet system).

Illuminators

The ink jet recorder of this embodiment preferably includes anilluminator to cure UV curable inks deposited onto the recording media.

In the embodiment illustrated in FIG. 2, illuminators 50 are disposed onthe carriage 70 that is mounted on the mobile unit 20, on both ends ofthe head 40 in the first direction. However, the configuration is notlimited thereto and the illuminators may be disposed at any locations aslong as UV radiation may be illuminated to the ink deposited on therecording surface of the recording medium P. For example, theilluminators may be disposed on the sides of the head 40 in the seconddirection so as to illuminate along the width direction (the firstdirection) of the recording medium, or such a configuration may be usedin combination with the illuminators 50 disposed at the positionsillustrated in FIG. 2.

The illuminator 50 includes a light source (not shown) and a lightsource controlling circuit (not shown) that controls switching on andoff of the light source. The light source is preferably a UV emittingdiode. In this case, the increase in the size and weight of the lightsource may be avoided compared to when other light sources such asmercury lamps, metal halide lamps or other types of lamps are used,thereby reducing the load incurred during the movement of the mobileunit 20.

When UV emitting diodes are used as the light sources, the emission peakwavelength of emitted UV radiation may be appropriately in the range of350 to 420 nm.

In order to increase the curing rate, to suppress the occurrence ofcuring wrinkles and to reduce the energy consumption, the illuminationintensity of the illuminators is preferably 500 mW/cm² to 2000 mW/cm²,and more preferably 700 mW/cm² to 2000 mW/cm².

When the ink is cured by illumination with the illuminators, theillumination energy is preferably 100 mJ/cm² to 2000 mJ/cm², morepreferably 200 mJ/cm² to 1500 mJ/cm², still more preferably 200 mJ/cm²to 1000 mJ/cm², and particularly preferably 200 mJ/cm² to 800 mJ/cm² inorder to ensure sufficient curing and to reduce the energy consumption.

Maintenance Unit

The ink jet recorder of this embodiment preferably has a maintenanceunit. The maintenance unit is a mechanism used for the maintenance ofthe head to prevent the occurrence of problems such as nozzle clogging.The maintenance unit is preferably mounted on the mobile unit 20,whereby the head may be maintained during the driving of the mobile unit20.

Examples of the operations for the maintenance of the head 40 include amoisture retention operation in which the head 40 is capped with the cap60 to prevent the vaporization of the ink except when recording is beingperformed, a flushing operation in which the ink is discharged from thenozzles of the head 40 to the ink tray 65 to prevent the nozzle cloggingwith the viscous ink as well as to adjust the meniscus of the nozzlesand allow the ink to be normally ejected from the head 40, a vacuumoperation (head cleaning) in which after the head 40 is capped with thecap 60, a vacuum pump (not shown) is driven to forcibly suction theviscous ink and foreign matters such as dusts that have become attachedto the nozzles, and thereby the meniscus is adjusted to allow the ink tobe normally ejected from the head 40, and a wiping operation with apurge treatment in which the nozzle face of the head 40 is wiped with awiper (not shown) to remove the ink which has become attached around thenozzles or has become viscous as well as to destroy the meniscus of thenozzles and readjust the meniscus.

As illustrated in FIG. 2, the cap 60 is disposed at one end of themobile unit 20 in the first direction, and the ink tray 65 is disposedat the other end in the first direction. However, the configuration isnot limited thereto, and these members may be disposed at any locationsas long as they are mounted on the mobile unit 20 and do not interferewith the recording operation of the head 40.

In order to reduce the load incurred during the movement of the mobileunit 20, it is preferable that the maintenance units mounted on themobile unit 20 be lightweight. For example, the mass of the maintenanceunits is preferably not more than 5 kg, and more preferably not morethan 3 kg. The lower limit is, although not limited to, preferably notless than 0.5 kg, and more preferably not less than 1 kg.

Further, it is preferable that the initial mass of the ink per onecontainer be smaller than the mass of the maintenance units mounted onthe mobile unit 20. This configuration reduces the influence by theincreased mass of the mobile unit 20 due to the increase in the numberof containers as compared to by the mass of the maintenance units. Thus,the number of containers mounted on the mobile unit 20 may be increased.In this embodiment, the specific gravity of the ink is defined to beapproximately 1 and thus, when the initial volume of the ink in thecontainer is 700 ml, the initial mass is 700 g. When the specificgravity of the ink is other than 1, the initial mass of the ink may beobtained by multiplying the initial volume of the ink in the containerby the specific gravity of the ink.

The maintenance unit is any one or more of a cap 60, a vacuum pump (notshown), an ink tray 65 and a wiper (not shown). When two or more of suchunits are used, the mass of the maintenance units is the total mass ofthe units.

Heating Units

In the use of UV curable inks (in particular, substantially water-freeUV curable inks described later), it is usually necessary that the highink viscosity be lowered before ejection. Because of this need, heatingunits that heat the ink to lower the viscosity to a level suited forejection are often disposed at, for example, containers 30, supply tubesand a head 40. In the use of UV curable inks, however, it is often thecase that a mobile unit 20 in a printer 1 carries members such asilluminators 50 and maintenance units described above in addition to thehead 40. Thus, the weight of the mobile unit 20 tends to be increased.

In order to reduce the increase in weight of the mobile unit 20, the inkjet recorder of the invention is configured such that the mobile unit 20is free from heating units (such as electrical heaters) that heat theink and lower the ink viscosity. Thus, the weight reduction of themobile unit 20 may be realized.

The invention does not eliminate the possibility that heating units bedisposed at any locations in the printer 1 except on the mobile unit 20.However, an ink viscosity suited for ejection may be obtained withoutheating by using UV curable inks having a preferred compositiondescribed later, and thus no heating units will be necessary on theprinter 1. The absence of heating units on the printer 1 advantageouslyallows the printer 1 to be miniaturized and simplified.

1.2. UV Curable Inks

UV curable inks are used in the ink jet recorder of this embodiment.With UV curable inks, records may be favorably produced on suchrecording media as glasses, acrylics and metals.

Hereinbelow, components which may be contained in the UV curable inksused in the ink jet recorder of this embodiment will be described indetail.

1.2.1. Polymerizable Compounds

The UV curable inks in this embodiment preferably contain apolymerizable compound. Upon illumination with light, the polymerizablecompound is polymerized by itself or by the action of aphotopolymerization initiator described later, and the deposited ink isthus cured.

Hereinbelow, the polymerizable compounds which may be used in the UVcurable inks in this embodiment will be described with respect tomonofunctional (meth)acrylates and polymerizable compounds other thanthe monofunctional (meth)acrylates (hereinafter, also referred to as“additional polymerizable compounds”). In the invention, the term“(meth)acrylic acid” refers to both acrylic acid and methacrylic acid,and the term “(meth)acrylate” refers to both acrylate and methacrylate.

Monofunctional (Meth)Acrylates

The UV curable inks in this embodiment preferably contain amonofunctional (meth)acrylate. A low viscosity may be obtained when theUV curable ink contains a monofunctional (meth)acrylate, and thus the UVcurable inks may be ejected without disposing heating units on theaforementioned ink jet recorder.

The content of the monofunctional (meth)acrylate is preferably 40 mass %to 90 mass %, more preferably 55 mass % to 80 mass %, and still morepreferably 60 mass % to 80 mass % with respect to the total mass of theink (100 mass %). When the content of the monofunctional (meth)acrylateis 40 mass % or above, a low viscosity may be easily obtained and thusthe UV curable inks attain a viscosity suited for the ejection in theink jet recorder. When the content of the monofunctional (meth)acrylateis 90 mass % or below, the viscosity of the UV curable inks does notbecome excessively low and consequently the occurrence of problems suchas curing wrinkles on images may be suppressed.

Hereinbelow, the monofunctional (meth)acrylates will be described withrespect to vinyl ether group-containing (meth)acrylates andmonofunctional (meth)acrylates other than the vinyl ethergroup-containing (meth)acrylates (hereinafter, also referred to as“further monofunctional (meth)acrylates”).

Specific examples of the vinyl ether group-containing (meth)acrylatesinclude compounds represented by General Formula (I) below.

CH₂═CR¹—COOR²—O—CH═CH—R³  (I)

In Formula (I), R¹ is a hydrogen atom or a methyl group, R² is adivalent organic residue having 2 to 20 carbon atoms, and R³ is ahydrogen atom or a monovalent organic residue having 1 to 11 carbonatoms.

The vinyl ether group-containing (meth)acrylate gives excellentcurability to the ink and lowers the viscosity of the ink. Further, theuse of such a compound containing a vinyl ether group and a(meth)acrylic group in the molecule is more advantageous in achievinggood curability of the ink than the separate use of a compoundcontaining a vinyl ether group and a compound containing a (meth)acrylicgroup.

In General Formula (I), the divalent organic residue having 2 to 20carbon atoms which is represented by R² is preferably a linear, branchedor cyclic, and optionally substituted alkylene group having 2 to 20carbon atoms, an optionally substituted alkylene group having 2 to 20carbon atoms which has an oxygen atom derived from an ether bond and/oran ester bond in the structure, or an optionally substituted divalentaromatic group having 6 to 11 carbon atoms. Of these, alkylene groupshaving 2 to 6 carbon atoms such as ethylene group, n-propylene group,isopropylene group and butylene group; and alkylene groups having 2 to 9carbon atoms which have an oxygen atom derived from an ether bond in thestructure such as oxyethylene group, oxy-n-propylene group,oxyisopropylene group and oxybutylene group are preferably used.

In General Formula (I), the monovalent organic residue having 1 to 11carbon atoms which is represented by R³ is preferably a linear, branchedor cyclic, and optionally substituted alkyl group having 1 to 10 carbonatoms, or an optionally substituted aromatic group having 6 to 11 carbonatoms. Of these, alkyl groups having 1 to 2 carbon atoms such as methylgroup and ethyl group, and aromatic groups having 6 to 8 carbon atomssuch as phenyl group and benzyl group are preferably used.

For the organic residues which may be substituted, the substituents areclassified into groups having carbon atoms and groups having no carbonatoms. In the first case in which the substituents are groups havingcarbon atoms, the carbon atoms in the substituents are included in thenumber of the carbon atoms in the organic residues. Examples of thegroups containing carbon atoms include, although not limited to,carboxyl groups and alkoxy groups. In the second case, examples of thegroups having no carbon atoms include, although not limited to, hydroxylgroup and halo groups.

Examples of the vinyl ether group-containing (meth)acrylates include,although not limited to, 2-vinyloxyethyl (meth)acrylate,3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl(meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl(meth)acrylate, 1-methyl-3-vinyloxypropyl (meth)acrylate,1-vinyloxymethylpropyl (meth)acrylate, 2-methyl-3-vinyloxypropyl(meth)acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth)acrylate,3-vinyloxybutyl (meth)acrylate, 1-methyl-2-vinyloxypropyl(meth)acrylate, 2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl(meth)acrylate, 6-vinyloxyhexyl (meth)acrylate,4-vinyloxymethylcyclohexylmethyl (meth)acrylate,3-vinyloxymethylcyclohexylmethyl (meth)acrylate,2-vinyloxymethylcyclohexylmethyl (meth)acrylate,p-vinyloxymethylphenylmethyl (meth)acrylate,m-vinyloxymethylphenylmethyl (meth)acrylate,o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(vinyloxyethoxy)ethyl(meth)acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyethoxy)propyl (meth)acrylate, 2-(vinyloxyethoxy)isopropyl(meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyethoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyethoxy)propyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyethoxyethoxy)isopropyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)isopropyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,polyethylene glycol monovinyl ether (meth)acrylate, and polypropyleneglycol monovinyl ether (meth)acrylate.

Of these, 2-(vinyloxyethoxy)ethyl (meth)acrylate, namely, at least oneof 2-(vinyloxyethoxy)ethyl acrylate and 2-(vinyloxyethoxy)ethylmethacrylate is preferable, and 2-(vinyloxyethoxy)ethyl acrylate is morepreferable because these (meth)acrylates can decrease the ink viscosityto a lower level, have a high ignition point and are excellent in termsof curability of the ink. In particular, the ink viscosity can bedecreased to a markedly low level because 2-(vinyloxyethoxy)ethylacrylate and 2-(vinyloxyethoxy)ethyl methacrylate have simple structuresand low molecular weights. Examples of the 2-(vinyloxyethoxy)ethylmethacrylates include 2-(2-vinyloxyethoxyl)ethyl methacrylate and2-(1-vinyloxyethoxyl)ethyl methacrylate. Examples of the2-(vinyloxyethoxy)ethyl acrylates include 2-(2-vinyloxyethoxyl)ethylacrylate and 2-(1-vinyloxyethoxyl)ethyl acrylate. The2-(vinyloxyethoxy)ethyl acrylates outperform the 2-(vinyloxyethoxy)ethylmethacrylates in terms of curability.

The vinyl ether group-containing (meth)acrylates may be used singly, ortwo or more may be used in combination.

The content of the vinyl ether group-containing (meth)acrylate (inparticular, 2-(vinyloxyethoxy)ethyl (meth)acrylate) is preferably 20mass % to 90 mass %, more preferably 40 mass % to 80 mass %, and stillmore preferably 50 mass % to 75 mass % with respect to the total mass ofthe UV curable ink (100 mass %). This lower limit of the content ensuresthat the ink viscosity may be lowered and the curability of the ink maybe further enhanced. On the other hand, the upper limit of the contentensures that good storage stability of the ink may be maintained and theoccurrence of curing wrinkles may be prevented further effectively.

Examples of the methods for producing the vinyl ether group-containing(meth)acrylates include, although not limited to, the esterification of(meth)acrylic acid with a hydroxyl group-containing vinyl ether(production method B), the esterification of a (meth)acrylic acid halidewith a hydroxyl group-containing vinyl ether (production method C), theesterification of (meth)acrylic acid anhydride with a hydroxylgroup-containing vinyl ether (production method D), thetransesterification between a (meth)acrylic acid ester and a hydroxylgroup-containing vinyl ether (production method E), the esterificationof (meth)acrylic acid with a halogen-containing vinyl ether (productionmethod F), the esterification of an alkali (or alkaline earth) metal(meth)acrylate with a halogen-containing vinyl ether (production methodG), the vinyl exchange reaction of a hydroxyl group-containing(meth)acrylic acid ester with vinyl carboxylate (production method H),and the ether exchange reaction of a hydroxyl group-containing(meth)acrylic acid ester with an alkyl vinyl ether (production methodI). Of these methods, the production method E is preferable because theadvantageous effects according to this embodiment are enhanced.

The UV curable ink in this embodiment may contain a furthermonofunctional (meth)acrylate instead of or in addition to the vinylether group-containing (meth)acrylate. By containing the furthermonofunctional (meth)acrylate, the ink shows a low viscosity and allowsa photopolymerization initiator and other additives to exhibit excellentsolubility in the ink. Further, the use of the further monofunctional(meth)acrylate facilitates obtaining good ejection stability during inkjet recording, and enhances the toughness, the heat resistance and thechemical resistance of the obtainable records.

Examples of the further monofunctional (meth)acrylates includephenoxyethyl (meth)acrylate, isoamyl (meth)acrylate, stearyl(meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, decyl(meth)acrylate, isomyristyl (meth)acrylate, isostearyl (meth)acrylate,2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate,4-hydroxybutyl (meth)acrylate, butoxyethyl (meth)acrylate,ethoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol(meth)acrylate, methoxypolyethylene glycol (meth)acrylate,methoxypropylene glycol (meth)acrylate, tetrahydrofurfuryl(meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate,2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl(meth)acrylate, lactone-modified flexible (meth)acrylate,t-butylcyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate,dicyclopentenyloxyethyl (meth)acrylate, benzyl (meth)acrylate,ethoxylated nonylphenyl (meth)acrylate, alkoxylated nonylphenyl(meth)acrylate, and p-cumyl phenol EO-modified (meth)acrylate.

Of these further monofunctional (meth)acrylates, those monofunctional(meth)acrylates having an aromatic ring backbone in the molecule arepreferable because further improvements are obtained in curability,storage stability and solubility of photopolymerization initiators.Preferred examples of the further monofunctional (meth)acrylates havingan aromatic ring backbone include, although not limited to, phenoxyethyl(meth)acrylate, benzyl (meth)acrylate, 2-hydroxyphenoxypropyl(meth)acrylate and phenoxydiethylene glycol (meth)acrylate. Of these, atleast one of phenoxyethyl (meth)acrylate and benzyl (meth)acrylate ispreferable, and phenoxyethyl (meth)acrylate is more preferable becausethe ink viscosity may be reduced as well as because excellent propertiesare obtained in terms of all of curability, abrasion resistance,adhesion and solubility of photopolymerization initiators.

The further monofunctional (meth)acrylates may be used singly, or two ormore may be used in combination.

The content of the further monofunctional (meth)acrylate is preferably10 mass % to 50 mass %, and more preferably 20 mass % to 40 mass % withrespect to the total mass of the UV curable ink (100 mass %). This lowerlimit of the content ensures that the solubility of aphotopolymerization initiator in addition to curability will be furtherenhanced. On the other hand, the upper limit of the content ensures thatthe adhesion in addition to curability will be further enhanced.

Additional Polymerizable Compounds

The UV curable ink in this embodiment may contain a polymerizablecompound other than the monofunctional (meth)acrylates described above,namely, may contain an “additional polymerizable compound”.

The additional polymerizable compounds may be any of various knownmonofunctional, difunctional, trifunctional and higher functionalmonomers and oligomers. Examples of the monomers include unsaturatedcarboxylic acids such as (meth)acrylic acid, itaconic acid, crotonicacid, isocrotonic acid and maleic acid as well as salts and estersthereof, urethanes, amides and anhydrides thereof, acrylonitrile,styrene, various unsaturated polyesters, unsaturated polyethers,unsaturated polyamides and unsaturated urethanes. Examples of theoligomers include oligomers formed of the above monomers such as linearacrylic oligomers, and epoxy (meth)acrylates, oxetane (meth)acrylates,aliphatic urethane (meth)acrylates, aromatic urethane (meth)acrylatesand polyester (meth)acrylates.

Of the additional polymerizable compounds, difunctional and higherfunctional (meth)acrylic acid esters, namely, difunctional and higherfunctional (meth)acrylates are preferable, and difunctional tohexafunctional (meth)acrylates are more preferable.

Examples of the difunctional (meth)acrylates include diethylene glycoldi(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethyleneglycol di(meth)acrylate, polyethylene glycol di(meth)acrylate,dipropylene glycol di(meth)acrylate, tripropylene glycoldi(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanedioldi(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanedioldi(meth)acrylate, neopentyl glycol di(meth)acrylate,dimethylol-tricyclodecane di(meth)acrylate, bisphenol A EO (ethyleneoxide) adduct di(meth)acrylate, bisphenol A PO (propylene oxide) adductdi(meth)acrylate, neopentyl glycol hydroxypivalate di(meth)acrylate, andpolytetramethylene glycol di(meth)acrylate.

Examples of the trifunctional and higher functional (meth)acrylatesinclude trimethylolpropane tri(meth)acrylate, EO-modifiedtrimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate,pentaerythritol tetra(meth)acrylate, dipentaerythritolhexa(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, glycerinpropoxy tri(meth)acrylate, caprolactone-modified trimethylolpropanetri(meth)acrylate, pentaerythritolethoxy tetra(meth)acrylate, andcaprolactam-modified dipentaerythritol hexa(meth)acrylate.

The additional polymerizable compounds may be used singly, or two ormore may be used in combination.

From such viewpoints as curability, suppression of curing wrinkles andsolubility of photopolymerization initiators, the content of theadditional polymerizable compound (in particular, difunctional or higherfunctional (meth)acrylate), if any contained in the UV curable ink, ispreferably 5 mass % to 45 mass %, more preferably 5 mass % to 35 mass %,and still more preferably 5 mass % to 30 mass % with respect to thetotal mass of the UV curable ink (100 mass %). In the case where the inkcontains an additional polymerizable compound that is a trifunctional orhigher functional (meth)acrylate, the content thereof is preferably 5mass % to 20 mass %, more preferably 5 mass % to 15 mass %, and stillmore preferably 5 mass % to 10 mass % with respect to the total mass ofthe ink (100 mass %).

In particular, a viscosity suited for ink jet recording (for example, 20mPa·s or less at 20° C.) may be easily obtained by the use of a UVcurable ink containing 40 mass % to 90 mass % of a monofunctional(meth)acrylate and 5 mass % to 45 mass % of a difunctional or higherfunctional (meth)acrylate.

Curing wrinkles are probably caused when the curing inside the inkproceeds slower than the curing of the ink surface and consequently theink surface is deformed by the progress of the curing inside the ink. Inthis embodiment, such curing wrinkles are advantageously suppressed whenthe UV curable ink contains a difunctional or higher functional(meth)acrylate.

The addition of photopolymerization initiators may be omitted by usingphotopolymerizable compounds as the polymerizable compounds. However,the use of photopolymerization initiators is more advantageous becausethe initiation of polymerization may be easily controlled.

1.2.2. Photopolymerization Initiators

The UV curable ink in this embodiment preferably contains aphotopolymerization initiator. The photopolymerization initiator may beused to induce photopolymerization by the illumination with UV radiationand to cure the ink deposited on the recording surface of the recordingmedium, thereby forming a print. The use of ultraviolet (UV) radiationis advantageous over other radiations because of its safety as well asbecause the costs of light source lamps may be saved. Thephotopolymerization initiators which may be used are not limited as longas active species such as radicals or cations are generated by theapplication of UV energy to induce the polymerization of thepolymerizable compounds. Radical or cation photopolymerizationinitiators may be used. In particular, radical photopolymerizationinitiators may be preferably used.

Examples of the radical photopolymerization initiators include aromaticketones, acylphosphine oxide compounds, aromatic onium salt compounds,organic peroxides, thio compounds (such as thioxanthone compounds andthiophenyl group-containing compounds), hexaarylbiimidazole compounds,ketoxime ester compounds, borate compounds, azinium compounds,metallocene compounds, active ester compounds, compounds having acarbon-halogen bond, and alkylamine compounds. Of these, acylphosphineoxide compounds are preferable because the curability of the ink may befurther enhanced particularly when UV emitting diodes are used.

Specific examples of the radical photopolymerization initiators includeacetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenylketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone,benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole,3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone,4,4′-diaminobenzophenone, Michler's ketone, benzoin propyl ether,benzoin ethyl ether, benzyl dimethyl ketal,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one,2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone,diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one,bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide,2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide,2,4-diethylthioxanthone, andbis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

Examples of commercially available radical photopolymerizationinitiators include IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethan-1-one),IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173(2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959(1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one),IRGACURE 127(2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propan-1-one),IRGACURE 907 (2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one),IRGACURE 369(2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1), IRGACURE379(2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone),DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE819 (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide), IRGACURE 784(bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium),IRGACURE OXE 01 (1,2-octanedione, 1-[4-(phenylthio)-,2-(0-benzoyloxime)]), IRGACURE OXE 02 (ethanone,1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(0-acetyloxime)),IRGACURE 754 (a mixture of oxyphenyl acetic acid2-[2-oxo-2-phenylacetoxyethoxy]ethyl ester and oxyphenyl acetic acid2-(2-hydroxyethoxyl)ethyl ester) (product names, manufactured by BASF),KAYACURE DETX-S (2,4-diethylthioxanthone) (product name, manufactured byNippon Kayaku Co., Ltd.), Speedcure TPO(2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), Speedcure DETX(2,4-diethylthioxanthen-9-one) (product names, manufactured by Lambson),Lucirin TPO, LR8893, LR8970 (product names, manufactured by BASF), andUBECRYL P36 (product name, manufactured by UCB).

The photopolymerization initiators may be used singly, or two or moremay be used in combination.

In order to ensure that the UV curing rate is increased and excellentcurability is obtained as well as to prevent incomplete dissolution ofthe photopolymerization initiator and to prevent coloring ascribed tothe photopolymerization initiator, the content of thephotopolymerization initiator is preferably not more than 20 mass % withrespect to the total mass of the UV curable ink (100 mass %).Particularly in the case in which the photopolymerization initiatorincludes an acylphosphine oxide compound, the content thereof is morepreferably 5 mass % to 15 mass %, and still more preferably 7 mass % to13 mass % with respect to the total mass of the UV curable ink (100 mass%). This lower limit of the content ensures that curability is furtherenhanced. In more detail, the curability is further enhanced because asufficient curing rate is obtained during curing particularly with UVemitting diodes (preferably having an emission peak wavelength of 350 nmto 420 nm). On the other hand, the upper limit of the content ensuresthat the solubility of the photopolymerization initiator is furtherenhanced.

1.2.3. Coloring Materials

The UV curable ink in this embodiment may contain a coloring material.The coloring material may be at least one of a pigment and a dye.

By using a pigment as the coloring material, the light resistance of theink may be enhanced. The pigments may be any of inorganic pigments andorganic pigments.

Examples of the inorganic pigments which may be used include carbonblacks (C.I. pigment black 7) such as furnace black, lamp black,acetylene black and channel black, iron oxide and titanium oxide.

Examples of the organic pigments include azo pigments such as insolubleazo pigments, condensed azo pigments, azo lakes and chelate azopigments; polycyclic pigments such as phthalocyanine pigments, peryleneand perinone pigments, anthraquinone pigments, quinacridone pigments,dioxane pigments, thioindigo pigments, isoindolinone pigments andquinophthalone pigments; dye chelates (such as basic dye chelates andacidic dye chelates), dye lakes (basic dye lakes and acidic dye lakes),nitro pigments, nitroso pigments, aniline blacks, and daylightfluorescent pigments.

The pigments may be used singly, or two or more may be used incombination.

When the pigment is used, the average particle diameter thereof ispreferably not more than 300 nm, and is more preferably 50 nm to 200 nm.This average particle diameter ensures that the ink is further enhancedin terms of reliability such as ejection stability and dispersionstability as well as that high quality images may be formed. In thespecification, the average particle diameter may be measured by adynamic light scattering method.

The dyes are not particularly limited, and any of acidic dyes, directdyes, reactive dyes and basic dyes may be used. The dyes may be usedsingly, or two or more may be used in combination.

1.2.4. Dispersants

In the case where the UV curable ink in this embodiment contains thepigment, the ink may further contain a dispersant to enhance thedispersibility of the pigment. The dispersants are not particularlylimited. For example, dispersants generally used to prepare pigmentdispersions such as polymer dispersants may be used. Specific examplesthereof include those which contain at least one main component selectedfrom polyoxyalkylene polyalkylene polyamines, vinyl polymers andcopolymers, acrylic polymers and copolymers, polyesters, polyamides,polyimides, polyurethanes, amino polymers, silicon-containing polymers,sulfur-containing polymers, fluorine-containing polymers and epoxyresins. Examples of commercially available polymer dispersants includeAJISPER series (product names) manufactured by Ajinomoto Fine-TechnoCo., Inc., Solsperse series (such as Solsperse 32000 and 36000 (productnames)) available from Avecia Co., DISPERBYK series (product names)manufactured by BYK Chemie, and DISPARLON series (product names)manufactured by KUSUMOTO Chemicals, Ltd.

The dispersants may be used singly, or two or more may be used incombination. The content of the dispersants is not particularly limited,and the dispersants may be appropriately added in suitable amounts.

1.2.5. Polymerization Inhibitors

The ink in this embodiment may contain a polymerization inhibitor. Thepresence of a polymerization inhibitor in the ink prevents thepolymerization reaction of the polymerizable compounds before curing.

The polymerization inhibitors are not particularly limited. For example,phenolic polymerization inhibitors may be used. Examples of the phenolicpolymerization inhibitors include, although not limited to,p-methoxyphenol, cresol, t-butylcatechol, di-t-butylparacresol,hydroquinone monomethyl ether, α-naphthol,3,5-di-t-butyl-4-hydroxytoluene, 2,6-di-t-butyl-4-methylphenol,2,2′-methylene-bis(4-methyl-6-t-butylphenol),2,2′-methylene-bis(4-ethyl-6-butylphenol), and4,4′-thio-bis(3-methyl-6-t-butylphenol).

Examples of commercially available phenolic polymerization inhibitorsinclude p-methoxyphenol (manufactured by Tokyo Chemical Industry Co.,Ltd., product name, p-methoxyphenol), NONFLEX MBP (manufactured by SeikoChemical Co., Ltd., product name,2,2′-methylene-bis(4-methyl-6-t-butylphenol)) and BHT SWANOX(manufactured by Seiko Chemical Co., Ltd., product name,2,6-di-t-butyl-4-methylphenol).

The polymerization inhibitors may be used singly, or two or more may beused in combination. The content of the polymerization inhibitors is notparticularly limited, and the polymerization inhibitors may beappropriately added in suitable amounts.

1.2.6. Surfactants

The UV curable ink in this embodiment may further contain a surfactant.The surfactants are not particularly limited. For example, siliconesurfactants such as polyester-modified silicones and polyether-modifiedsilicones may be used. It is particularly preferable to usepolyether-modified polydimethylsiloxane or polyester-modifiedpolydimethylsiloxane. Examples of commercially available slipping agentsinclude BYK-347, BYK-348, and BYK-UV3500, 3510, 3530 and 3570(manufactured by BYK).

The surfactants may be used singly, or two or more may be used incombination. The content of the surfactants is not particularly limited,and the surfactants may be appropriately added in suitable amounts.

1.2.7. Other Additives

The UV curable ink in this embodiment may contain additives (components)other than the aforementioned additives. Such components are notparticularly limited. Examples include known polymerizationaccelerators, penetration enhancers, wetting agents (humectants), andfurther additives. Examples of the further additives include knownfixing agents, mildew-proofing agents, preservatives, antioxidants, UVabsorbers, chelating agents, pH adjusters and thickening agents.

The UV curable ink in this embodiment is preferably a nonaqueous UVcurable ink. The term “nonaqueous UV curable ink” refers to a UV curableink designed to be free from water. In detail, the content of water inthe UV curable ink is preferably not more than 3 mass %, more preferablynot more than 1 mass %, still more preferably less than 0.05 mass %,even more preferably less than 0.01 mass %, further preferably less than0.005 mass %, and most preferably less than 0.001 mass %. Such an inkmay be also referred to as a substantially water-free UV curable inkcomposition.

1.2.8. Properties of UV Curable Inks Illumination Energy

When the UV curable inks described above are used, it is preferable touse such UV curable inks which are cured with illumination energy of notmore than 1000 mJ/cm², more preferably not more than 300 mJ/cm², stillmore preferably not more than 200 mJ/cm², and particularly preferablynot more than 100 mJ/cm² from the viewpoint that the power consumptionby the illuminators may be saved.

Viscosity

The viscosity of the UV curable inks at 20° C. is preferably not morethan 20 mPa·s, and is more preferably 4 mPa·s to 13 mPa·s, and stillmore preferably 7 mPa·s to 13 mPa·s. With this viscosity, the ink jetrecorder may be used in a usual environment without the need of heatingunits, and consequently the ink jet recorder may be miniaturized orsimplified. The viscosity of the UV curable inks may be measured with anE-type viscometer.

The viscosity of the UV curable inks at ejection from the head ispreferably not more than 20 mPa·s, and is more preferably 4 mPa·s to 13mPa·s, and still more preferably 7 mPa·s to 13 mPa·s. With thisconfiguration in which the viscosity of the UV curable inks duringejection is not more than 20 mPa·s, the head of the ink jet recorder mayachieve good ejection stability. When the viscosity of the UV curableinks during ejection is not less than 4 mPa·s, the occurrence ofproblems such as curing wrinkles on the recorded images may be reduced,and thus satisfactory images may be obtained. The viscosity of the UVcurable inks may be measured with an E-type viscometer.

The temperature of the UV curable inks at the time of ejection from thehead is preferably not more than 35° C., and more preferably not morethan 30° C. The lower limit temperature is preferably 10° C. or above,more preferably 15° C. or above, and still more preferably 20° C. orabove. In this case, the ink jet recorder may be appropriately placed insuch an environment that the temperature of the UV curable inks willfall in the above range. The above temperature of the UV curable inksensures that the viscosity of the UV curable inks during ejection willbe easily maintained in the aforementioned preferred range.

In order to control the viscosity of the UV curable inks in the aboverange, the proportions of components in the ink may be appropriatelyadjusted. For example, the viscosity of the aforementioned UV curableinks may be controlled by controlling the proportions of thepolymerizable compounds.

1.3. Recording Media

The ink jet recorder of this embodiment may be used for the recording onany types of recording media used in flat-bed ink jet recorders (such aspapers, woven articles, knitted articles, nonwoven fabrics, leathers,resin films, resin sheets, glasses and metals). In particular, the inkjet recorder fitted with the aforementioned hot swapping mechanism mayproduce records on any of these recording media with satisfactory imagequality with a reduced probability of failures such as misaligned imagesor variations in color tone. Thus, the inventive ink jet recorder may besuitably used even for the recording on expensive recording media (suchas metals, acrylics and glasses) where a significant loss is incurred inthe event of recording failure.

The recording medium used in the flat-bed ink jet recorder is a singlesheet. For example, the length of the recording surface in the seconddirection when the sheet is supported on the panel of the support unit10 may be not more than 4 m, particularly not more than 3 m and may benot less than 0.5 m, particularly not less than 1 m.

2. Examples

Hereinbelow, the embodiments of the first aspect of the invention willbe described in further detail based on Examples. However, theembodiments are not limited to such Examples.

2.1. Evaluation of Inks 2.1.1. Preparation of Inks

Components described in Table 1 were mixed in the contents described inTable 1, and the mixtures were each stirred with a high-speedwater-cooled stirrer to give UV curable inks (hereinafter, also referredto simply as “inks”) 1 to 10. The components shown in Table 1 are thefollowing.

Polymerizable Compounds

VEEA (product name, 2-(2-vinyloxyethoxyl)ethyl acrylate, manufactured byNippon Shokubai Co., Ltd., monofunctional (meth)acrylate, hereinafter“VEEA”)

BISCOAT #192 (product name, phenoxyethyl acrylate, manufactured by OsakaOrganic Chemical Industry Ltd., monofunctional (meth)acrylate,hereinafter “PEA”)

V #160 (product name, benzyl acrylate, manufactured by Osaka OrganicChemical Industry Ltd., monofunctional (meth)acrylate, hereinafter“BZA”)

IBXA (product name, isobornyl acrylate, manufactured by Osaka OrganicChemical Industry Ltd., monofunctional (meth)acrylate, hereinafter“IBX”)

SR508 (product name, dipropylene glycol diacrylate, difunctional(meth)acrylate, manufactured by Sartomer)

A-DPH (product name, dipentaerythritol hexaacrylate, hexafunctional(meth)acrylate, manufactured by SHIN-NAKAMURA CHEMICAL CO., LTD.,hereinafter “A-DPH”) Polymer

BISCOAT #1000 (product name, manufactured by Osaka Organic ChemicalIndustry Ltd., hyperbranched polymer, viscosity: 273 mPa·s, number ofacrylic groups: 14, hereinafter “V #1000”)

BISCOAT #1000 is a hyperbranched polymer in which functional groups arebranched from dipentaerythritol as the core, and contains ethyleneglycol diacrylate as a diluent monomer.

Photopolymerization Initiators

IRGACURE 819 (product name, manufactured by BASF, solid content: 100%,hereinafter “819”)

DAROCUR TPO (product name, manufactured by Lambson, hereinafter “TPO”)

IRGACURE 369 (product name, manufactured by BASF, hereinafter “369”)

Surfactant

BYK-UV3500 (product name, manufactured by BYK, polyether-modifiedpolydimethylsiloxane, hereinafter “BYK3500”)

Coloring Material

C.I. pigment black 7 (manufactured by Mitsubishi Chemical Corporation,Mitsubishi Carbon MA11, hereinafter “PB-7”)

Dispersant

Solsperse 32000 (product name, manufactured by Avecia Co., hereinafter“S0L32000”)

Polymerization Inhibitor

P-methoxyphenol (product name, manufactured by Tokyo Chemical IndustryCo., Ltd., p-methoxyphenol, hereinafter “MEHQ”)

TABLE 1 Components Ink 1 Ink 2 Ink 3 Ink 4 Ink 5 Ink 6 Ink 7 Ink 8 Ink 9Ink 10 Polymerizable VEEA 50 20 87.7 77.7 82.7 42.7 60 55 50 compoundsPEA 30 30 5 42.7 15 30 BZA 20 IBX 10 SR508 30 45 45 A-DPH 7.7 7.7 7.77.7 7.7 Polymer V#1000 10 Photopolymerization 819 4 4 4 4 4 4 4 4 4initiators TPO 5 5 5 5 5 5 5 5 5 369 9 Surfactant BYK3500 0.2 0.2 0.20.2 0.2 0.2 0.2 0.2 0.2 0.2 Coloring material PB-7 2 2 2 2 2 2 2 2 2 2Dispersant SOL32000 1 1 1 1 1 1 1 1 1 1 Polymerization MEHQ 0.1 0.1 0.10.1 0.1 0.1 0.1 0.1 0.1 0.1 inhibitor Total 100 100 100 100 100 100 100100 100 100 Evaluation results Ranks of ink viscosity 2 3 1 2 1 2 2 2 22 at 20° C. Storage stability A A A B A A B A A A Curability A A A C A CC A B C

2.1.2. Ink Evaluation Tests Viscosity Evaluation (Ranking of InkViscosity at 20° C.)

With a DVM-E-type rotational viscometer (manufactured by TOKYO KEIKIINC.), each of the inks prepared above was tested to determine theviscosity at 20° C. The rotor used was a DVM-E-type cone having a coneangle of 1° 34′ and a cone radius of 2.4 cm. The rotational speed was 10rpm. The evaluation criteria were as follows. The evaluation results aredescribed in Table 1.

1: Less than 7 mPa·s.

2: 7 mPa·s to 13 mPa·s.

3: More than 13 mPa·s.

Storage Stability Evaluation

Each of the inks prepared above was placed into a 50 cc volume glassbottle, and the bottle was tightly closed. Thereafter, the glass bottleswere placed in a thermostatic chamber and were allowed to stand at 60°C. for 7 days. After 7 days, the glass bottles were removed and wereallowed to cool sufficiently to room temperature. Subsequently, theviscosity was measured at 20° C. in the same manner as the aboveevaluation “ranking of ink viscosity at 20° C.”. The rate of increase ofthe viscosity after the 7 days storage relative to the initial viscosity(immediately after preparation) was calculated. The evaluation criteriawere as follows. The evaluation results are described in Table 1.

A: Not more than +5%.

B: More than +5%.

Ink Curability Evaluation

Each of the inks was applied onto LUMIRROR #125-E20 (product name,manufactured by TORAY INDUSTRIES, INC., PET film) with a bar coatermanufactured by TESTER SANGYO CO., LTD. The thickness of the film aftercuring was 10 μm. Next, the ink was illuminated with UV radiation at adose of 1,000 mW/cm² with an LED having a peak wavelength of 395 nm(Firefly (product name), manufactured by Phoseon) for a prescribed timeto give a cured ink film. After the irradiation, the surface of the inkfilm was rubbed back and forth 20 times with a cotton swab manufacturedby Johnson & Johnson K.K. under a load of 130 g. The illumination energyrequired for the ink film to be free from abrasion marks was measured.The evaluation criteria were as follows. The evaluation results aredescribed in Table 1.

A: Not more than 200 mJ/cm².

B: More than 200 mJ/cm² to 300 mJ/cm².

C: More than 300 mJ/cm².

2.1.3. Ink Evaluation Results

The results of the above ink evaluations are collectively set forth inTable 1.

As described in Table 1, it has been demonstrated that both excellentstorage stability and excellent curability were achieved by the inks 1,2, 8 and 9 which contained a vinyl ether group-containing (meth)acrylicacid ester of General Formula (I) and a monofunctional (meth)acrylateother than the vinyl ether group-containing (meth)acrylic acid ester andwhich had a viscosity at 20° C. of not less than 7 mPa·s.

Further, as described in Table 1, the ink 2 has been demonstrated tohave high viscosity at 20° C., and the inks 3 and 5 have been shown tohave low viscosity at 20° C. Thus, it has been shown that the inkviscosity is variable in accordance with the proportions ofpolymerizable compounds.

From the evaluation results of the curability of the ink 1 and the ink 9in Table 1, it has been demonstrated that the ink curability is enhancedby the use of an acylphosphine oxide compound as the photopolymerizationinitiator.

2.2. Evaluation of Ink Jet Recorders 2.2.1. Preparation of Recorders

Prior to the testing of recorders, the following recorders 1 to 6 wereprepared. The recorders 1 to 3 were made by modifying GS6000 (productname, manufactured by SEIKO EPSON CORPORATION, large format printer) insuch a manner that the stand and the recording medium transport devicewere removed, and wheels and a drive unit were attached to the remainingbody to form a mobile unit, which was then movably mounted on a supportunit. The mobile unit was configured to be moved on their wheels on thesupport unit in the second direction by driving of the drive unit. Themobile unit had maintenance units (a cap for tightly closing the head, avacuum pump for suctioning the ink in the head, and a wiper for wipingthe nozzle face of the head) at one end in the head travel direction(the first direction), as well as had an ink tray on the other end forreceiving the ink pushed out by flushing. The total mass of themaintenance units mounted on the mobile unit was 3 kg (except in therecorders 4 and 5 described later). Further, a notebook computer forcreating print data was mounted on the cabinet of the mobile unit (seeFIG. 2).

The length of a supply tube (an ink supply tube) connecting the inkcartridge to the head was 6 m in the recorder 3 and was 3 m in the otherrecorders.

Recorder 1

In the recorder 1, two identical color ink cartridges were mounted onthe mobile unit (namely, the hot swapping function was added).

Recorder 2

In the recorder 2, one ink cartridge was mounted on the mobile unit(namely, the hot swapping function was not added).

Recorder 3

In the recorder 3, two identical color ink cartridges were mounted onthe support unit (namely, the hot swapping function was added, but theink cartridges were not moved together with the mobile unit).

Recorder 4

The recorder 4 was GS6000 on which two identical color ink cartridgeswere mounted (namely, the recorder was a usual large format printerwhich had the hot swapping function but did not include any mobile unitor support unit).

Recorder 5

The recorder 5 was prepared by removing the maintenance units from themobile unit in the recorder 1 and attaching them to the outside of thesupport unit in the first direction.

Recorder 6

The recorder 6 was similar to the recorder 1, except that the notebookcomputer for creating print (image) data was not mounted on the mobileunit but was placed on a desk disposed aside the support unit, andconsequently the mobile unit was connected to the notebook computer viaa longer wire cord (a USB cable) than in the recorder 1.

Illuminators

Further, the following illuminators 1 to 3 were selected and mounted onthe recorders 1 to 6 according to the combinations described in Tables 2and 3.

The illuminators 1 included illuminators A for preliminary curingdisposed at both ends of the head in the first direction, andilluminators B for main curing disposed on the second direction sides ofthe head so as to illuminate along the width direction of the recordingmedium. In all the illuminators A and B, the illumination intensity was1000 mW/cm² and the light sources were UV emitting diodes.

The configuration of the illuminators 2 was similar to the illuminators1, except that the illumination intensity was 500 mW/cm².

The configuration of the illuminators 3 was similar to the illuminators1, except that the UV emitting diodes were replaced by metal halidelamps.

Inks

The inks prepared as described hereinabove were added to ink cartridges,which were then mounted on the recorders as described in Tables 2 and 3.

2.2.2. Evaluation of Recorders Printing Continuity Performance

The ink was supplied to the head from the ink cartridge mounted on therecorder. As mentioned earlier, two identical color ink cartridges weremounted on the recorders 1, 3, 4, 5 and 6, whilst one ink cartridge wasmounted on the recorder 2. A recording medium, which was an acrylicsheet having an area described in Table 2 or 3, was set onto the panelof the support unit.

Recording was then started to produce a 1.1×2.3 m² solid pattern image.In Example in which the recording medium had an area of 2.1×3.5 m², a2.0×3.5 m² solid pattern image was recorded. In Example which involvedthe recorder 4, a roll of flexible vinyl chloride paper was set and a1.1×6.9 m² continuous pattern was recorded. The thickness of the inkfilm after the printing of the solid pattern was 10 μm. After the solidpattern image was recorded, a new sheet of the recording medium was setonto the stage. These operations were repeated to produce similarrecords on fifty sheets of the recording medium. When one of thecartridges had become empty when a new sheet of the recording medium wasset, the empty cartridge was replaced by the new cartridge. In thismanner, the printing continuity performance was evaluated. Theevaluation criteria were as follows. The evaluation results aredescribed in Tables 2 and 3.

Here, the term “solid pattern image” refers to an image pattern whichshould be usually such that the recording region of the recording mediumhas been filled in with the ink and consequently the true character ofthe recording medium is hidden by the recording of ink dots for all thepixels which are the smallest recording units defined in terms ofrecording resolution.

A: The first cartridge lasted until the images were recorded on thirtysheets of the recording medium. Because of the hot swapping function,every sheet of the recording medium was printed without any interruptionof the ink supply during the recording.B: The cartridges were exchanged before the image was recorded on the30th or earlier sheet of the recording medium. Because of the hotswapping function, every sheet of the recording medium was printedwithout any interruption of the ink supply during the recording.C: The ink in the cartridge was spent during the recording on any onesheet of the recording medium, and the printing had to be interruptedfor the exchange of cartridges.

Cleaning Properties

The ink was supplied to the head from the ink cartridge mounted on therecorder. After the head was filled with the ink, the cartridge wasremoved and the ink was suctioned through the head to empty the inksupply tube. Thereafter, a cartridge containing a cleaning solution(diethylene glycol ethyl ether acetate) was attached, and the cleaningsolution was suctioned from the head and was discharged through thehead. The transmittance was measured with respect to every 5 cc of thecleaning solution discharged from the head, and the amount of thedischarged cleaning solution was accumulated until the transmittance ofthe discharged cleaning solution reached 98% or more of thetransmittance of the cleaning solution in the cartridge before cleaning.In this manner, cleaning properties were evaluated. The transmittancewas measured with a spectrophotometer (product name “U-3300”,manufactured by Hitachi, Ltd.) with respect to the discharged cleaningsolution diluted 1000 times by the addition of distilled water. Theevaluation criteria were as follows. The evaluation results aredescribed in Tables 2 and 3.

◯: Not more than 300 cc.

x: More than 300 cc.

Fill-in Properties in Solid Pattern Image (Solid Fill Evaluation)

On a PET film (product name “LUMIRROR 125 E20”, manufactured by TORAYINDUSTRIES, INC.) as the recording medium, 11 ng/pixel dots were formedand cured, thereby recording a solid pattern image having a recordingresolution of 720 dpi×720 dpi and a dimension (size) of 20 cm×20 cm. Thepixels are the smallest recording units defined in terms of recordingresolution. During recording, the main scanning (pass) was performed inwhich the ink was ejected from the head while the carriage on which thehead was mounted was moved in the first direction, and the ink depositedon the recording medium was illuminated with illumination energy of 50mJ/cm² per pass. After the main scanning, the ink was illuminatedseveral times by moving the carriage in the first direction until thetotal of illumination energy per unit area of the recording mediumreached 1000 mJ/cm². The recording medium was then visually inspectedfrom a distance of 30 cm to determine whether or not the dots in thesolid pattern image region failed to hide any portion of the recordingsurface. The evaluation criteria were as follows. The evaluation resultsare described in Tables 2 and 3.

A: The recording surface was not visible.

B: The recording surface was visible.

Curing Wrinkles

The solid pattern images obtained in the above evaluation “Fill-inproperties in solid pattern image” were used. Each solid pattern imagewas analyzed with laser microscope VK-9700 (manufactured by KEYENCE) todetermine the root mean square height (Rq). Further, the surface of thesolid pattern image was visually observed. The evaluation criteria wereas follows. The evaluation results are described in Tables 2 and 3.

A: Rq was not more than 4. The solid pattern image had gloss on thesurface.

B: Rq was more than 4 and not more than 6. The solid pattern image hadslight gloss on the surface.

C: Rq was more than 6. The solid pattern image did not show gloss on thesurface.

2.2.3. Recorder Evaluation Results

The results of the recorder evaluation tests are described in Tables 2and 3.

TABLE 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 RecorderInk used 1 1 1 1 2 1 10 4 6 configuration Recorder used 1 1 1 1 1 1 1 11 Illuminators 1 1 1 1 1 1 3 1 1 used Initial volume 700 300 2000 700700 700 700 700 700 in ink container (ml) Recording medium 1.2 × 2.4 1.2× 2.4 1.2 × 2.4 2.1 × 3.5 1.2 × 2.4 1.2 × 2.4 1.2 × 2.4 1.2 × 2.4 1.2 ×2.4 area (m × m) Ink temperature during 25° C. 25° C. 25° C. 25° C. 35°C. 30° C. 25° C. 25° C. 25° C. ejection Ranks of ink viscosity during 22 2 2 2 2 2 2 2 ejection Evaluation Cleaning ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ resultsproperties Printing A B A B A A A A A continuity performance Solid fillA A A A B A A A A evaluation (solid pattern) Curing A A A A A A A B Awrinkles Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17Recorder Ink used 7 8 9 3 5 1 1 1 configuration Recorder used 1 1 1 1 11 5 6 Illuminators used 1 1 1 1 1 2 1 1 Initial volume in ink 700 700700 700 700 700 700 700 container (ml) Recording medium area (m × m) 1.2× 2.4 1.2 × 2.4 1.2 × 2.4 1.2 × 2.4 1.2 × 2.4 1.2 × 2.4 1.2 × 2.4 1.2 ×2.4 Ink temperature during ejection 25° C. 25° C. 25° C. 25° C. 25° C.25° C. 25° C. 25° C. Ranks of ink viscosity during 2 2 2 1 1 2 2 2ejection Evaluation Cleaning properties ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ results Printingcontinuity A A A A A A A A performance Solid fill evaluation A A A A A AA A (solid pattern) Curing wrinkles A A A C C C A A

TABLE 3 Comp. Ex. 1 Comp. Ex. 2 Comp. Ex. 3 Ref. Ex. 1 Ref. Ex. 2 Ref.Ex. 3 Recorder Ink used 1 1 1 1 10 2 configuration Recorder used 2 2 3 41 1 Illuminators used 1 1 1 1 1 1 Initial volume in ink container (ml)700 1000 700 700 700 700 Recording medium area (m × m) 1.2 × 2.4 1.2 ×2.4 1.2 × 2.4 1.2 × 2.4 1.2 × 2.4 1.2 × 2.4 Ink temperature duringejection 25° C. 25° C. 25° C. 25° C. 25° C. 30° C. Ranks of inkviscosity during ejection 2 2 2 2 2 3 Evaluation Cleaning properties ◯ ◯X ◯ ◯ — results Printing continuity performance C C B A — — Solid fillevaluation (solid pattern) A A A A — — Curing wrinkles A A A A — —

As shown in the evaluation results in Table 2, the recorders in Examplesachieved good printing (recording) continuity performance because ofhaving the hot swapping function. Further, the hot swapping functionreduced the occurrence of image failures such as misaligned images orvariations in color tone. Furthermore, because the recorders in Exampleshad the ink cartridges mounted on the mobile unit, the length of the inksupply tubes connecting the ink cartridges to the head was short andconsequently the amount of the cleaning solution used was saved.

In more detail, Example 2 required frequent exchanges of ink cartridgesbecause the ink cartridges used had small volumes, but the hot swappingfunction allowed every sheet of the recording medium to be printedwithout any interruption of the ink supply during the recording.

Example 3 involved large-volume ink cartridges. As a result, a high loadwas incurred for the movement of the mobile unit because of the weightincrease of the mobile unit.

In Example 4, the recording medium used had a large area of therecording surface, and consequently the ink cartridge exchange frequencywas increased.

In Example 5, the ink had a high viscosity and was used after beingheated with a heater. As a result, the weight of the mobile unit wasincreased and a high load was incurred for the movement of the mobileunit. The decrease in fill-in properties was probably because the inkviscosity was increased after ejection from the head.

Example 6 involved metal halide lamps as the illumination devices. As aresult, the weight of the mobile unit was increased by the installationof illuminator cooling devices, and a high load was incurred for themovement of the mobile unit. Further, the recording medium had beenthermally deformed by heating with the metal halide lamps.

In Examples 13 and 14, the occurrence of curing wrinkles tended to bemarked because of the low viscosity of the ink used.

In Example 15, the occurrence of curing wrinkles tended to be markedbecause of the low illumination intensity.

In Example 16, the maintenance units were not mounted on the mobile unitand thus failed to perform the flushing operation during the recordingon any one sheet of the recording medium. Because the maintenance unitswere disposed under constant light irradiation outside the gantrycabinet, the discharged ink which had become attached to the cap and theink tray increased its viscosity and was resistant to removal.

A similar configuration as in Example 1 was produced, except thatauxiliary maintenance units were further mounted on the mobile unit as abackup that performs the maintenance of the head in case of breakdown ofthe maintenance units. The total mass of the maintenance units was 6 kg,and the mobile unit could not be moved because of such a heavy load forthe movement of the mobile unit.

In Example 17, the notebook computer was not mounted on the mobile unitand thus was connected to the mobile unit via a long wire cord (a USBcable). This configuration resulted in a necessity that the wires bedisposed at a position permitting a smooth operation.

As described in Table 3, the recorders in Comparative Examples 1 and 2did not have the hot swapping function and were unsatisfactory inprinting (recording) continuity performance. Further, the recordedimages had problems such as misalignment or varied color tone.

Although the recorder in Comparative Example 3 had the hot swappingfunction, the mobile unit did not carry any ink cartridges and thus theink supply tubes connecting the ink cartridges to the head were long.Consequently, as described in Table 3, cleaning of the ink supplychannels required a large amount of the cleaning solution.

The recorder in Reference Example 1 failed to perform printing on hardrecording media such as acrylic sheets.

The recorders used in Reference Examples 2 and 3 performed well, but theimplementation of the evaluations was infeasible due to the inks used.Specifically, the ink in Reference Example 2 did not cure, and the inkin Reference Example 3 could not be ejected due to such a highviscosity.

The invention is not limited to these embodiments described hereinabove,and various modifications are possible. For example, the scope of theinvention includes configurations substantially identical to thosedescribed in the embodiments (for example, configurations having thesame functions, approaches and results, or configurations having thesame objects and effects). Further, the scope of the invention includesconfigurations resulting from the substitution of non-essentialcomponents in the aforementioned embodiments with other components.Furthermore, the scope of the invention includes configurations thatachieve the same effects or the same objects as the configurationsdescribed in the embodiments. The scope of the invention also includescombinations of the configurations described in the aforementionedembodiments and known configurations.

2. Examples

Hereinbelow, the embodiments of the second aspect of the invention willbe described in further detail based on Examples. However, theembodiments are not limited to such Examples.

2.1. Evaluation of Inks 2.1.1. Preparation of Inks

Components described in Table 4 were mixed in the contents described inTable 4, and the mixtures were each stirred with a high-speedwater-cooled stirrer to give UV curable inks (hereinafter, also referredto simply as “inks”) 1 to 11. The components shown in Table 4 are thefollowing.

Polymerizable Compounds

VEEA (product name, 2-(2-vinyloxyethoxyl)ethyl acrylate, manufactured byNippon Shokubai Co., Ltd., monofunctional (meth)acrylate, hereinafter“VEEA”)

BISCOAT #192 (product name, phenoxyethyl acrylate, manufactured by OsakaOrganic Chemical Industry Ltd., monofunctional (meth)acrylate,hereinafter “PEA”)

V #160 (product name, benzyl acrylate, manufactured by Osaka OrganicChemical Industry Ltd., monofunctional (meth)acrylate, hereinafter“BZA”)

IBXA (product name, isobornyl acrylate, manufactured by Osaka OrganicChemical Industry Ltd., monofunctional (meth)acrylate, hereinafter“IBX”)

SR508 (product name, dipropylene glycol diacrylate, difunctional(meth)acrylate, manufactured by Sartomer)

A-DPH (product name, dipentaerythritol hexaacrylate, hexafunctional(meth)acrylate, manufactured by SHIN-NAKAMURA CHEMICAL CO., LTD.,hereinafter “A-DPH”) Polymer

BISCOAT #1000 (product name, manufactured by Osaka Organic ChemicalIndustry Ltd., hyperbranched polymer, viscosity: 273 mPa·s, number ofacrylic groups: 14, hereinafter “V #1000”)

BISCOAT #1000 is a hyperbranched polymer in which functional groups arebranched from dipentaerythritol as the core, and contains ethyleneglycol diacrylate as a diluent monomer.

Photopolymerization Initiators

IRGACURE 819 (product name, manufactured by BASF, solid content: 100%,hereinafter “819”)

DAROCUR TPO (product name, manufactured by Lambson, hereinafter “TPO”)

IRGACURE 369 (product name, manufactured by BASF, hereinafter “369”)

Surfactant

BYK-UV3500 (product name, manufactured by BYK, polyether-modifiedpolydimethylsiloxane, hereinafter “BYK3500”)

Coloring Material

C.I. pigment black 7 (manufactured by Mitsubishi Chemical Corporation,Mitsubishi Carbon MA11, hereinafter “PB-7”)

Dispersant

Solsperse 32000 (product name, manufactured by Avecia Co., hereinafter“SOL32000”)

Polymerization Inhibitor

P-methoxyphenol (product name, manufactured by Tokyo Chemical IndustryCo., Ltd., p-methoxyphenol, hereinafter “MEHQ”)

TABLE 4 Components Ink 1 Ink 2 Ink 3 Ink 4 Ink 5 Ink 6 Ink 7 Ink 8 Ink 9Ink 10 Ink 11 Polymerizable VEEA 50 87.7 77.7 82.7 42.7 60 55 50 40 7compounds PEA 30 5 42.7 15 30 10 54.7 BZA 20 IBX 10 SR508 45 45 29.7 26A-DPH 7.7 7.7 7.7 7.7 8 Polymer V#1000 10 Photopolymerization 819 4 4 44 4 4 4 4 4 4 initiators TPO 5 5 5 5 5 5 5 5 5 5 369 9 SurfactantBYK3500 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Coloring materialPB-7 2 2 2 2 2 2 2 2 2 2 2 Dispersant SOL32000 1 1 1 1 1 1 1 1 1 1 1Polymerization MEHQ 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1inhibitor Total 100 100 100 100 100 100 100 100 100 100 100 Evaluationresults Ranks of ink viscosity at 2 1 2 1 2 2 2 2 2 3 4 20° C. Storagestability A A B A A B A A A B A Curability A A C A C C A B C A B

2.1.2. Ink Evaluation Tests Viscosity Evaluation (Ranking of InkViscosity at 20° C.)

With a DVM-E-type rotational viscometer (manufactured by TOKYO KEIKIINC.), each of the inks prepared above was tested to determine theviscosity at 20° C. The rotor used was a DVM-E-type cone having a coneangle of 1° 34′ and a cone radius of 2.4 cm. The rotational speed was 10rpm. The evaluation criteria were as follows. The evaluation results aredescribed in Table 4.

1: Less than 7 mPa·s.

2: 7 mPa·s to 13 mPa·s.

3: More than 13 mPa·s to 20 mPa·s.

4: More than 20 mPa·s.

Storage Stability Evaluation

Each of the inks prepared above was placed into a 50 cc volume glassbottle, and the bottle was tightly closed. Thereafter, the glass bottleswere placed in a thermostatic chamber and were allowed to stand at 60°C. for 7 days. After 7 days, the glass bottles were removed and wereallowed to cool sufficiently to room temperature. Subsequently, theviscosity was measured at 20° C. in the same manner as the aboveevaluation “ranking of ink viscosity at 20° C.”. The rate of increase ofthe viscosity after the 7 days storage relative to the initial viscosity(immediately after preparation) was calculated. The evaluation criteriawere as follows. The evaluation results are described in Table 4.

A: Not more than +5%.

B: More than +5%.

Ink Curability Evaluation

Each of the inks was applied onto LUMIRROR #125-E20 (product name,manufactured by TORAY INDUSTRIES, INC., a PET film) with a bar coatermanufactured by TESTER SANGYO CO., LTD. The thickness of the film aftercuring was 10 μm. Next, the ink was illuminated with UV radiation at adose of 1,000 mW/cm² with an LED having a peak wavelength of 395 nm(Firefly (product name), manufactured by Phoseon) for a prescribed timeto give a cured ink film. After the irradiation, the surface of the inkfilm was rubbed back and forth 20 times with a cotton swab manufacturedby Johnson & Johnson K.K. under a load of 130 g. The illumination energyrequired for the ink film to be free from abrasion marks was measured.The evaluation criteria were as follows. The evaluation results aredescribed in Table 4.

A: Not more than 200 mJ/cm².

B: More than 200 mJ/cm² to 300 mJ/cm².

C: More than 300 mJ/cm².

2.1.3. Ink Evaluation Results

The results of the above ink evaluations are collectively set forth inTable 4.

As described in Table 4, it has been demonstrated that both excellentstorage stability and excellent curability were achieved by the inks 1,7, 8, 10 and 11 which contained a vinyl ether group-containing(meth)acrylate of General Formula (I), a monofunctional (meth)acrylateother than the vinyl ether group-containing (meth)acrylate, and anacylphosphine oxide compound and which had a viscosity at 20° C. of notless than 7 mPa·s.

From the viscosity evaluation results, the viscosity at 20° C. of theinks 2 and 4 was low, and the viscosity at 20° C. of the inks 10 and 11was high. Thus, it has been shown that the ink viscosity is variable inaccordance with the proportions of polymerizable compounds.

From the evaluation results of the curability of the ink 1 and the ink9, it has been demonstrated that the ink curability with LEDillumination is enhanced by the use of an acylphosphine oxide compoundas the photopolymerization initiator.

2.2. Evaluation of Ink Jet Recorders 2.2.1. Preparation of Recorders

Prior to the testing of recorders, the following recorders 1 to 6 wereprepared. The recorders 1 to 3 were made by modifying GS6000 (productname, manufactured by SEIKO EPSON CORPORATION, large format printer) insuch a manner that the stand and the recording medium transport devicewere removed, and illuminators described later, wheels and a drive unitwere attached to the remaining body to form a mobile unit, which wasthen movably mounted on a support unit. The mobile unit was configuredto be moved on their wheels on the support unit in the second directionby driving of the drive unit. The mobile unit had maintenance units (acap for tightly closing the head, a vacuum pump for suctioning the inkin the head, and a wiper for wiping the nozzle face of the head) at oneend in the head travel direction (the first direction), as well as hadan ink tray on the other end for receiving the ink pushed out byflushing. The total mass of the maintenance units mounted on the mobileunit was 3 kg (except in the recorder 5 described later). Further, anotebook computer for creating print data was mounted on the cabinet ofthe mobile unit (see FIG. 2, except in the recorder 6 described later).

The length of a supply tube (an ink supply tube) connecting the inkcartridge to the head was 6 m in the recorder 3 and was 3 m in the otherrecorders.

Recorder 1

In the recorder 1, an ink cartridge was mounted on the mobile unit.Further, any heating units were not mounted on the recorder 1 (namely,no heating units were mounted at any locations in the recorder 1including the mobile unit).

Recorder 2

In the recorder 2, an ink cartridge and a heating unit were mounted onthe mobile unit. In detail, temperature control medium go and returnchannels were disposed as the heating unit adjacent to the ink supplytube extending from the cartridge to the head. Diethylene glycol wascirculated through the temperature control medium circulating channels.A temperature control medium tank was disposed in the temperaturecontrol medium circulating channels, and a heater was fitted to the tankto heat the temperature control medium. Thus, the heating unit wasconfigured such that the ink running through the ink supply tube wouldbe heated by the temperature control medium in the adjacent temperaturecontrol medium circulating channels, and the temperature was controlledwith a heater controller such that the temperature of the ink beingejected from the head would be a temperature described in the table. Theheating unit was disposed on the mobile unit except on the head. Aseparate head heater was attached in the head.

Recorder 3

In the recorder 3, an ink cartridge was mounted on the support unit(namely, the ink cartridge was not moved together with the mobile unit).Further, any heating units were not mounted on the recorder 3 (namely,no heating units were mounted at any locations in the recorder 3including the mobile unit).

Recorder 4

The recorder 4 was GS6000 without modification except that illuminatorswere mounted thereon (namely, the recorder was a usual large formatprinter which did not include any mobile unit or support unit). Further,any heating units were not mounted on the recorder 4.

Recorder 5

The recorder 5 was prepared by removing the maintenance units from themobile unit in the recorder 1 and attaching them to the outside of thesupport unit in the first direction.

Recorder 6

The recorder 6 was similar to the recorder 1, except that the notebookcomputer for creating print (image) data was not mounted on the mobileunit but was placed on a desk disposed aside the support unit, andconsequently the mobile unit was connected to the notebook computer viaa longer wire cord (a USB cable) than in the recorder 1.

Illuminators

The following illuminators 1 to 3 were selected and mounted on therecorders 1 to 6 according to the combinations described in Tables 5 and6.

The illuminators 1 were disposed on the carriage, and includedilluminators A for preliminary curing that were disposed at both ends ofthe head in the first direction, and illuminators B for main curing thatwere disposed on the second direction sides of the head so as toilluminate along the width direction of the recording medium. In all theilluminators A and B, the illumination intensity was 1000 mW/cm² and thelight sources were UV emitting diodes.

The configuration of the illuminators 2 was similar to the illuminators1, except that the illumination intensity was 500 mW/cm².

The configuration of the illuminators 3 was similar to the illuminators1, except that the UV emitting diodes were replaced by metal halidelamps.

Inks

The inks prepared as described hereinabove were added to ink cartridges,which were then mounted on the recorders as described in Tables 5 and 6.

2.2.2. Evaluation of Recorders

The recorders were subjected to the following evaluations. In eachevaluation test, the recorders were placed in a laboratory controlled ata prescribed temperature. However, in Comparative Example 3, the inktemperature was adjusted with the heater in the recorder. To determinethe temperature of the ink being ejected from the head, the temperatureof the nozzle plate was measured with a thermometer (a thermocouple)immediately before the start of recording and was taken as the inktemperature.

Further, the ink viscosity during ejection was measured in the samemanner as in the above “Viscosity evaluation”, except that the viscositymeasurement temperature was the temperature of the ink being ejected.The thus-measured ink viscosity during ejection was ranked according tothe similar evaluation criteria as in the “Viscosity evaluation”, theresults being described in Tables 5 and 6.

Ejection Stability

After the ink was supplied to the head from the ink cartridge mounted onthe recorder, printing was started and the ink was continuously ejectedthrough 360 nozzles of the head for 5 minutes. After 5 minutes, theprinting was discontinued. Ejection stability was evaluated based on thenumber of nozzles that had become non-functioning in ink ejection(failed nozzles). The evaluation criteria were as follows. Theevaluation results are described in Tables 5 and 6.

◯: Five or less failed nozzles.

Δ: Six to ten failed nozzles.

x: Eleven or more failed nozzles.

Cleaning Properties

The ink was supplied to the head from the ink cartridge mounted on therecorder. After the head was filled with the ink, the cartridge wasremoved and the ink was suctioned through the head to empty the inksupply tube. Thereafter, a cartridge containing a cleaning solution(diethylene glycol ethyl ether acetate) was attached, and the cleaningsolution was suctioned from the head and was discharged through thehead. The transmittance was measured with respect to every 5 cc of thecleaning solution discharged from the head, and the amount of thedischarged cleaning solution was accumulated until the transmittance ofthe discharged cleaning solution reached 98% or more of thetransmittance of the cleaning solution in the cartridge before cleaning.In this manner, cleaning properties were evaluated. The transmittancewas measured with a spectrophotometer (product name “U-3300”,manufactured by Hitachi, Ltd.) with respect to the discharged cleaningsolution diluted 1000 times by the addition of distilled water. Theevaluation criteria were as follows. The evaluation results aredescribed in Tables 5 and 6.

◯: Not more than 300 cc.

x: More than 300 cc.

Fill-in Properties in Solid Pattern Image (Solid Fill Evaluation)

On a recording medium (product name “LUMIRROR 125 E20”, manufactured byTORAY INDUSTRIES, INC., a PET film), 11 ng/pixel dots were formed andcured, thereby recording a solid pattern image having a recordingresolution of 720 dpi×720 dpi and a dimension (size) of 20 cm×20 cm. Thepixels are the smallest recording units defined in terms of recordingresolution. During recording, the main scanning (pass) was performed inwhich the ink was ejected from the head while the carriage on which thehead was mounted was moved in the first direction, and the ink depositedon the recording medium was illuminated with illumination energy of 50mJ/cm² per pass. After the main scanning, the ink was illuminatedseveral times by moving the carriage in the first direction until thetotal of illumination energy per unit area of the recording mediumreached 1000 mJ/cm². The recording medium was then visually inspectedfrom a distance of 30 cm to determine whether or not the dots in thesolid pattern image region failed to hide any portion of the recordingsurface. The evaluation criteria were as follows. The evaluation resultsare described in Tables 5 and 6.

Here, the term “solid pattern image” refers to an image pattern whichshould be usually such that the recording region of the recording mediumhas been filled in with the ink and consequently the true character ofthe recording medium is hidden by the recording of ink dots for all thepixels which are the smallest recording units defined in terms ofrecording resolution.

A: The recording surface was not visible.

B: The recording surface was visible.

Curing Wrinkles

The solid pattern images obtained in the above evaluation “Fill-inproperties in solid pattern image” were used. Each solid pattern imagewas analyzed with laser microscope VK-9700 (manufactured by KEYENCE) todetermine the root mean square height (Rq). Further, the surface of thesolid pattern image was visually observed. The evaluation criteria wereas follows. The evaluation results are described in Tables 5 and 6.

A: Rq was not more than 4. The solid pattern image had gloss on thesurface.

B: Rq was more than 4 and not more than 6. The solid pattern image hadslight gloss on the surface.

C: Rq was more than 6. The solid pattern image did not show gloss on thesurface.

Weight Reduction of Mobile Unit

To evaluate the weight reduction of the mobile unit, the masses of themobile units in the recorders used in Examples and Comparative Exampleswere compared with the mass of the mobile unit in the recorder 1 used inExample 1 as the standard. In detail, the difference “Y−X (kg)” wascalculated wherein X was the mass (kg) of the mobile unit in therecorder 1 used in Example 1 and Y was the mass (kg) of the mobile unitused in any of Examples and Comparative Examples. The evaluationcriteria were as follows. The evaluation results are described in Tables5 and 6.

⊙: Y−X<−1

◯: −1≦Y−X≦1

Δ: 1<Y−X≦5

x: 5<Y−X

2.2.3. Recorder Evaluation Results

The results of the recorder evaluation tests are described in Tables 5and 6.

TABLE 5 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Recorder Inkused 1 1 2 3 4 5 6 7 configuration Recorder used 1 3 1 1 1 1 1 1Illuminators used 1 1 1 1 1 1 1 1 Ink temperature during ejection 25° C.25° C. 25° C. 25° C. 25° C. 25° C. 25° C. 25° C. Ranks of ink viscosityduring 2 2 1 2 1 2 2 2 ejection Evaluation Ejection stability ◯ ◯ ◯ ◯ ◯◯ ◯ ◯ results Cleaning ◯ X ◯ ◯ ◯ ◯ ◯ ◯ properties Solid fill evaluationA A A A A A A A (solid pattern) Curing wrinkles A A C B C A A A Weightreduction ◯ ⊙ ◯ ◯ ◯ ◯ ◯ ◯ of mobile unit Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex.13 Ex. 14 Ex. 15 Ex. 16 Recorder Ink used 8 9 9 10 1 1 1 1 configurationRecorder used 1 1 1 1 1 1 5 6 Illuminators used 1 1 3 1 1 2 1 1 Inktemperature during ejection 25° C. 25° C. 25° C. 30° C. 30° C. 25° C.25° C. 25° C. Ranks of ink viscosity during 2 2 2 3 2 2 2 2 ejectionEvaluation Ejection stability ◯ ◯ ◯ Δ ◯ ◯ ◯ ◯ results Cleaning ◯ ◯ ◯ ◯ ◯◯ ◯ ◯ properties Solid fill evaluation A — A A A A A A (solid pattern)Curing wrinkles A — A A A C A A Weight reduction ◯ ◯ Δ ◯ ◯ ◯ ⊙ ◯ ofmobile unit

TABLE 6 Comp. Ex. 1 Comp. Ex. 2 Comp. Ex. 3 Recorder Ink used 1 11 11configuration Recorder used 4 2 2 Illuminators used 1 1 1 Inktemperature during ejection 25° C. 25° C. 45° C. Ranks of ink viscosityduring ejection 2 4 2 Evaluation Ejection stability ◯ X ◯ resultsCleaning properties ◯ — ◯ Solid fill evaluation A — B (solid pattern)Curing wrinkles A — A Weight reduction of — X X mobile unit

As shown in the evaluation results in Table 5, the recorders in Examplesachieved weight reduction of the mobile unit because the mobile unit wasfree from heating units.

The recorder 3 used in Example 2 achieved further reduction in theweight of the mobile unit because the mobile unit did not carry the inkcartridge. However, the length of the ink supply tube connecting the inkcartridge to the head was extended, and consequently the amount of thecleaning solution used was increased.

In Examples 3 and 5, marked curing wrinkles occurred on the imagebecause of the low viscosity of the ink used.

In Example 10, the ink did not cure with LED illumination because theink 9 used did not contain an acylphosphine oxide compound as thephotopolymerization initiator. Consequently, the evaluations of fill-inproperties and curing wrinkles were infeasible.

Example 11 involved the recorder 1 which included the illuminators 3using metal halide lamps. Due to the weight increase by the installationof the metal halide lamps and illuminator cooling devices, the movementof the mobile unit incurred a higher load than in the use of UV emittingdiodes.

In Example 12, the ejection stability tended to be decreased because ofthe high viscosity of the ink used.

Example 14, which involved the illuminators 2 having an illuminationintensity of 500 mW/cm², resulted in the occurrence of marked curingwrinkles on the image.

The recorder 5 used in Example 15 achieved further reduction in theweight of the mobile unit because the mobile unit did not carry themaintenance units. However, this configuration made it impossible toperform the flushing operation during the recording on any one sheet ofthe recording medium. Further, because the maintenance units weredisposed outside the cabinet of the mobile unit and were exposed toconstant irradiation with fluorescent light in the room in which therecorder was disposed, the discharged ink which had become attached tothe cap and the ink tray increased its viscosity and was resistant toremoval.

In Example 16, the notebook computer was not mounted on the mobile unitand thus was connected to the mobile unit via a long wire cord (a USBcable). This configuration resulted in a necessity that the wires bedisposed at a position permitting a smooth operation.

The recorder 4 used in Comparative Example 1 failed to perform printingon hard recording media such as acrylic sheets.

Comparative Examples 2 and 3 involved the recorder 2 in which theheating unit was mounted on the mobile unit. Thus, the weight of themobile unit was significantly increased as compared to the recordersused in Examples.

Comparative Example 2 involved the ink 11 having a high viscosity.Because heating with the heating unit was not performed, the inkejection stability was significantly lowered.

In Comparative Example 3, the ink 11 having a high viscosity was usedafter being heated. As a result, good ejection stability was obtained.However, fill-in properties were deteriorated, probably because the inktemperature was decreased during the time from the ejection until theink landed on the recording medium, and consequently the ink viscositywas increased to make it difficult for the ink to spread on therecording medium. Further, the weight reduction of the mobile unit wasnot realized due to the installation of the heater.

The recorders used in Examples and Comparative Examples included asingle container for an ink having an individual composition. It hasbeen then found that the installation of a plurality of containerscontaining inks of identical composition in the mobile unit allows therecorder to print images without any interruption during recording of animage, at the price of weight increase of the mobile unit. However, theconfigurations in this embodiment make it possible to save the weight ofthe mobile unit as compared to when heating units are mounted on themobile unit. Thus, the particular usefulness of the configurations inthis embodiment has been demonstrated.

The invention is not limited to these embodiments described hereinabove,and various modifications are possible. For example, the scope of theinvention includes configurations substantially identical to thosedescribed in the embodiments (for example, configurations having thesame functions, approaches and results, or configurations having thesame objects and effects). Further, the scope of the invention includesconfigurations resulting from the substitution of non-essentialcomponents in the aforementioned embodiments with other components.Furthermore, the scope of the invention includes configurations thatachieve the same effects or the same objects as the configurationsdescribed in the embodiments. The scope of the invention also includescombinations of the configurations described in the aforementionedembodiments and known configurations.

What is claimed is:
 1. An ink jet recorder comprising: a support unitconfigured to support a recording medium, a container containing a UVcurable ink, and a mobile unit including a head configured to eject theUV curable ink supplied from the container, the mobile unit being freefrom a heating unit that heats the UV curable ink to lower theviscosity, the recorder being configured to record an image on therecording medium in such a manner that the head performs main scanningby ejecting the UV curable ink while changing positions in a firstdirection, and the mobile unit performs sub-scanning by moving in asecond direction intersecting with the first direction.
 2. The ink jetrecorder according to claim 1, wherein the viscosity of the UV curableink at 20° C. is not more than 20 mPa·s.
 3. The ink jet recorderaccording to claim 1, wherein the UV curable ink contains 40 mass % to90 mass % of a monofunctional (meth)acrylate, and 5 mass % to 45 mass %of a difunctional or higher functional (meth)acrylate.
 4. The ink jetrecorder according to claim 1, wherein the UV curable ink is anonaqueous UV curable ink.
 5. The ink jet recorder according to claim 1,wherein the temperature of the UV curable ink as ejected from the headis not more than 35° C.
 6. The ink jet recorder according to claim 1,wherein the mobile unit includes an illuminator including a UV emittingdiode to induce curing of the UV curable ink.
 7. The ink jet recorderaccording to claim 6, wherein the illuminator is configured to cure theUV curable ink deposited on the recording medium with illuminationenergy of 200 mJ/cm² to 1500 mJ/cm² by illuminating the ink with UVradiation having an emission peak wavelength in the range of 350 nm to420 nm.
 8. The ink jet recorder according to claim 1, wherein the UVcurable ink contains a photopolymerization initiator, and thephotopolymerization initiator includes an acylphosphine oxide compound.9. The ink jet recorder according to claim 1, wherein the mobile unitincludes one or more maintenance units configured to perform maintenanceof the head.